Error: Unable to update job

### Description

Error Message in Logfile:

[2018-11-15 21:53:04.7521] [I] [Core] .NET Core 4.6.27019.06 on Linux 4.15.0 #1
SMP Thu Aug 23 19:33:51 MSK 2018 [X64]
[2018-11-15 21:53:04.8335] [I] [Core] 43 coins loaded from /usr/src/miningcore/b
uild/coins.json
[2018-11-15 21:53:04.9642] [I] [ShareRecorder] Online
[2018-11-15 21:53:05.2499] [I] [Core] API Access to /api/admin restricted to 127
.0.0.1,::1,::ffff:127.0.0.1
[2018-11-15 21:53:05.2499] [I] [Core] API Access to /metrics restricted to 127.0
.0.1,::1,::ffff:127.0.0.1
[2018-11-15 21:53:05.3622] [I] [Core] API access limited to 5 requests per 1s, e
xcept from 127.0.0.1, ::1, ::ffff:127.0.0.1
[2018-11-15 21:53:05.3863] [I] [Core] API Online @ 0.0.0.0:4000
[2018-11-15 21:53:05.3867] [I] [Core] Prometheus Metrics Online @ 0.0.0.0:4000/m
etrics
[2018-11-15 21:53:05.3867] [I] [Core] WebSocket notifications streaming @ 0.0.0.
0:4000/notifications
[2018-11-15 21:53:05.3867] [I] [Core] Payment processing is not enabled
[2018-11-15 21:53:05.3917] [I] [StatsRecorder] Online
[2018-11-15 21:53:05.4279] [I] [xmr001] Starting Pool ...
[2018-11-15 21:53:05.4457] [I] [xmr001] Starting Job Manager ...
[2018-11-15 21:53:05.6149] [I] [xmr001] All daemons online
[2018-11-15 21:53:05.6818] [I] [xmr001] All daemons synched with blockchain
[2018-11-15 21:53:05.7862] [W] [xmr001] Error(s) refreshing network stats: One o
r more errors occurred. (Unexpected character encountered while parsing value: <
. Path '', line 0, position 0.) (Code -500)
[2018-11-15 21:53:05.8256] [I] [xmr001] Job Manager Online
[2018-11-15 21:53:06.4932] [I] [xmr001] Detected new block 1705863 via RPC polli
ng
[2018-11-15 21:53:06.5023] [I] [xmr001] Broadcasting job
[2018-11-15 21:53:07.2829] [I] [xmr001] Pool Online
[2018-11-15 21:53:07.2880] [I] [xmr001]

Mining Pool:            xmr001
Coin Type:              XMR [XMR]
Network Connected:      Main
Detected Reward Type:   POW
Current Block Height:   1705863
Current Connect Peers:  0
Network Difficulty:     55263729172
Network Hash Rate:      0 KH/s
Stratum Port(s):        3032, 3033, 3034
Pool Fee:               1,5%

[2018-11-15 21:53:07.2925] [I] [xmr001] Stratum ports 0.0.0.0:3032, 0.0.0.0:3033
, 0.0.0.0:3034 online
[2018-11-15 21:53:06.5023] [I] [xmr001] Broadcasting job
[2018-11-15 21:53:07.2829] [I] [xmr001] Pool Online
[2018-11-15 21:53:07.2880] [I] [xmr001]

Mining Pool:            xmr001
Coin Type:              XMR [XMR]
Network Connected:      Main
Detected Reward Type:   POW
Current Block Height:   1705863
Current Connect Peers:  0
Network Difficulty:     55263729172
Network Hash Rate:      0 KH/s
Stratum Port(s):        3032, 3033, 3034
Pool Fee:               1,5%

[2018-11-15 21:53:07.2925] [I] [xmr001] Stratum ports 0.0.0.0:3032, 0.0.0.0:3033, 0.0.0.0:3034 online
[2018-11-15 21:53:15.4037] [I] [StatsRecorder] Updating hashrates for pool xmr001
[2018-11-15 21:53:15.5925] [I] [StatsRecorder] Performing Stats GC
[2018-11-15 21:53:15.6047] [I] [StatsRecorder] Stats GC complete
[2018-11-15 21:53:29.7950] [I] [xmr001] [0HLIB7HISS412] Connection from ::ffff:111.111.111.111:57742 accepted on port 3034
[2018-11-15 21:53:29.8692] [I] [xmr001] [0HLIB7HISS412] Authorized miner XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
[2018-11-15 21:53:34.5159] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:55:08.5525] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:55:25.4928] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:55:47.2510] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:55:55.1305] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:56:17.2512] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:56:40.3727] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:56:44.3511] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:56:59.7143] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:57:02.1700] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:57:03.3910] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:57:04.9062] [I] [xmr001] Detected new block 1705864 via RPC polling
[2018-11-15 21:57:04.9066] [I] [xmr001] Broadcasting job
[2018-11-15 21:57:04.9547] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 21:57:36.8123] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 21:57:43.6506] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:57:54.0101] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 21:58:15.6050] [I] [StatsRecorder] Updating hashrates for pool xmr001
[2018-11-15 21:58:15.6206] [I] [StatsRecorder] Performing Stats GC
[2018-11-15 21:58:15.6206] [I] [StatsRecorder] Stats GC complete
[2018-11-15 21:58:17.8970] [I] [xmr001] Detected new block 1705865 via RPC polling
[2018-11-15 21:58:17.8970] [I] [xmr001] Broadcasting job

[...]

[2018-11-15 22:11:38.8930] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:11:38.9350] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:11:43.5666] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 22:12:01.3203] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:12:04.0181] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:12:23.2950] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:12:51.1532] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:12:51.2241] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:12:51.5297] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000
[2018-11-15 22:13:10.4230] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:13:10.5050] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:13:10.5460] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:13:10.5870] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:13:15.6433] [I] [StatsRecorder] Updating hashrates for pool xmr001
[2018-11-15 22:13:15.6522] [I] [StatsRecorder] Performing Stats GC
[2018-11-15 22:13:15.6528] [I] [StatsRecorder] Stats GC complete
[2018-11-15 22:13:15.9680] [I] [xmr001] Detected new block 1705875 via RPC polling
[2018-11-15 22:13:15.9680] [I] [xmr001] Broadcasting job
[2018-11-15 22:13:19.4622] [W] [xmr001] Unable to update job. Daemon responded with: One or more errors occurred. (Unexpected character encountered while parsing value: <. Path '', line 0, position 0.) Code -500
[2018-11-15 22:13:19.9308] [I] [xmr001] [0HLIB7HISS412] Share accepted: D=200000


### Steps to Reproduce

1. Build from current master branch
2. start daemon
3. start mining

### Version

current version from master branch
OS Ubuntu 18.04 

### Additional Information

my config:

root@h2810139:~# cat /usr/src/miningcore/build/config.json
{
    "logging": {
        "level": "info",
        "enableConsoleLog": true,
        "enableConsoleColors": true,
        // Log file name (full log) - can be null in which case log events are written to console (stdout)
        "logFile": "core.log",
        // Log file name for API-requests - can be null in which case log events are written to either main logFile or console (stdout)
        "apiLogFile": "api.log",
        // Folder to store log file(s)
        "logBaseDirectory": "/var/log/monero", // or c:\path\to\logs on Windows
        // If enabled, separate log file will be stored for each pool as <pool id>.log
        // in the above specific folder.
        "perPoolLogFile": false
    },
    "banning": {
        // "integrated" or "iptables" (linux only - not yet implemented)
        "manager": "integrated",
        "banOnJunkReceive": false,
        "banOnInvalidShares": false
    },
    "notifications": {
        "enabled": true,
        "email": {
            "host": "1111.1111.1111.111",
            "port": 25,
            "user": "xxxxx",
            "password": "xxxxxxxxx",
            "fromAddress": "xxxx@xxxxx.de",
            "fromName": "POOL-Server"
        },
        "admin": {
            "enabled": false,
            "emailAddress": "xxxx@xxxxx.de",
            "notifyBlockFound": true
        }
    },
    // Where to persist shares and blocks to
    "persistence": {
        // Persist to postgresql database
        "postgres": {
            "host": "127.0.0.1",
            "port": 5432,
            "user": "miningcore",
            "password": "xxxxxx",
            "database": "miningcore"
        }
    },
    // Generate payouts for recorded shares and blocks
    "paymentProcessing": {
        "enabled": false,
        // How often to process payouts, in milliseconds
        "interval": 600,
        // Path to a file used to backup shares under emergency conditions, such as
        // database outage
        "shareRecoveryFile": "/home/monero/recovered-shares.txt"
    },
    // API Settings
    "api": {
        "enabled": true,
        // Binding address (Default: 127.0.0.1)
        "listenAddress": "0.0.0.0",
        // Binding port (Default: 4000)
        "port": 4000,
        // IP address whitelist for requests to Prometheus Metrics (default 127.0.0.1)
        "metricsIpWhitelist": [],
        // Limit rate of requests to API on a per-IP basis
        "rateLimiting": {
            "disabled": false, // disable rate-limiting all-together, be careful
            // override default rate-limit rules, refer to https://github.com/stefanprodan/AspNetCoreRateLimit/wiki/IpRateLimitMiddleware#defining-rate-limit-rules
            "rules": [
                {
                    "Endpoint": "*",
                    "Period": "1s",
                    "Limit": 5
                }
            ],
            // List of IP addresses excempt from rate-limiting (default: none)
            "ipWhitelist": []
        }
    },
    "pools": [
        {
            // DON'T change the id after a production pool has begun collecting shares!
            "id": "xmr001",
            "enabled": true,
            "coin": "monero",
            // Address to where block rewards are given (pool wallet)
            "address": "xxxxxxxxxxxxxxxxxxx",
            // Block rewards go to the configured pool wallet address to later be paid out
            // to miners, except for a percentage that can go to, for examples,
            // pool operator(s) as pool fees or or to donations address. Addresses or hashed
            // public keys can be used. Here is an example of rewards going to the main pool
            // "op"
            "rewardRecipients": [
                {
                    // Pool wallet
                    "address": "xxxxxxxxxxxxxxxxxxxxxx",
                    "percentage": 1.5
                }
            ],
            // How often to poll RPC daemons for new blocks, in milliseconds
            "blockRefreshInterval": 500,
            // Some miner apps will consider the pool dead/offline if it doesn't receive
            // anything new jobs for around a minute, so every time we broadcast jobs,
            // set a timeout to rebroadcast in this many seconds unless we find a new job.
            // Set to zero to disable. (Default: 0)
            "jobRebroadcastTimeout": 10,
            // Remove workers that haven't been in contact for this many seconds.
            // Some attackers will create thousands of workers that use up all available
            // socket connections, usually the workers are zombies and don't submit shares
            // after connecting. This features detects those and disconnects them.
            "clientConnectionTimeout": 600,
            // If a worker is submitting a high threshold of invalid shares, we can
            // temporarily ban their IP to reduce system/network load.
            "banning": {
                "enabled": false,
                // How many seconds to ban worker for
                "time": 600,
                // What percent of invalid shares triggers ban
                "invalidPercent": 50,
                // Check invalid percent when this many shares have been submitted
                "checkThreshold": 50
            },
            // Each pool can have as many ports for your miners to connect to as you wish.
            // Each port can be configured to use its own pool difficulty and variable
            // difficulty settings. 'varDiff' is optional and will only be used for the ports
            // you configure it for.
        "ports": {
                "3032": {
                    "listenAddress": "0.0.0.0",
                    "difficulty": 7500,
                    "name": "CPU Mining",
                    "varDiff": {
                    "minDiff": 1000,
                    "maxDiff": null,
                    "targetTime": 15,
                    "retargetTime": 90,
                    "variancePercent": 30
                    }
                },
                "3033": {
                    "listenAddress": "0.0.0.0",
                    "difficulty": 25000,
                    "name": "GPU Mining",
                    "varDiff": {
                    "minDiff": 10000,
                    "maxDiff": null,
                    "targetTime": 15,
                    "retargetTime": 90,
                    "variancePercent": 30
                    }
                },
                "3034": {
                    "listenAddress": "0.0.0.0",
                    "difficulty": 200000,
                    "name": "High-End Multi GPU Mining",
                    "varDiff": {
                    "minDiff": 200000,
                    "maxDiff": null,
                    "targetTime": 15,
                    "retargetTime": 120,
                    "variancePercent": 30
                  }
                }
        },
            // Recommended to have at least two daemon instances running in case one drops
            // out-of-sync or offline. For redundancy, all instances will be polled for
            // block/transaction updates and be used for submitting blocks. Creating a backup
            // daemon involves spawning a daemon using the "-datadir=/backup" argument which
            // creates a new daemon instance with it's own RPC config. For more info on this,
            // visit: https:// en.bitcoin.it/wiki/Data_directory and
            // https:// en.bitcoin.it/wiki/Running_bitcoind
            "daemons": [
                {
                    "host": "127.0.0.1",
                    "port": 18081,
                    "user": "xxx",
                    "password": "xxx",
                    // Enable streaming Block Notifications via ZeroMQ messaging from Bitcoin
                    // Family daemons. Using this is highly recommended. The value of this option
                    // is a string that should match the value of the -zmqpubhashblock parameter
                    // passed to the coin daemon. If you enable this, you should lower
                    // 'blockRefreshInterval' to 1000 or 0 to disable polling entirely.
                    //"zmqBlockNotifySocket": "tcp://127.0.0.1:15101",

                    // Enable streaming Block Notifications via WebSocket messaging from Ethereum
                    // family Parity daemons. Using this is highly recommended. The value of this
                    // option is a string that should  match the value of the --ws-port parameter
                    // passed to the parity coin daemon. When using --ws-port, you should also
                    // specify --ws-interface all and
                    // --jsonrpc-apis "eth,net,web3,personal,parity,parity_pubsub,rpc"
                    // If you enable this, you should lower 'blockRefreshInterval' to 1000 or 0
                    // to disable polling entirely.
                    //"portWs": 18545,
                },
                {
                      "host": "127.0.0.1",
                      "port": 18082,
                      "user": "xxx",
                      "password": "xxx",
                      "category": "wallet"
                }
            ],
            // Generate payouts for recorded shares
            "paymentProcessing": {
                    "enabled": true,
                    "minimumPayment": 0.25,
                "minimumPaymentToPaymentId": 1.0,
                    "payoutScheme": "PPLNS",
                    "payoutSchemeConfig": {
                      "factor": 2.0
                    }
            }
        }
    ]
}