Debug 15% invalid shares
Thanks for the excellent piece of work that is this proxy. It is very fast and light on resources. I am using xmrig-proxy and seeing a 15% invalid shares. My understanding is that I am loosing hash-power this way. If this is correct (i.e. this is a problem) can you please help me debug and understand what is happening and what is the reason for those invalid shares ?

PS: The proxy is setting a fixed difficulty to upstream pool (using wallet+400000 method). Also the proxy is setting a fixed difficulty of 2500 to my CPU miners (roughly 140H/s) using this option `--custom-diff=2500`

```
[2018-02-25 18:13:29] #002 accepted (141242/59+17605) diff 400015 (30 ms)
[2018-02-25 18:13:29] #019 accepted (141243/59+17605) diff 400015 (7 ms)
[2018-02-25 18:13:29] #023 accepted (141244/59+17605) diff 400015 (33 ms)
[2018-02-25 18:13:30] #005 accepted (141245/59+17605) diff 400015 (8 ms)
[2018-02-25 18:13:30] #019 accepted (141246/59+17605) diff 400015 (8 ms)
[2018-02-25 18:13:31] #019 accepted (141247/59+17605) diff 400015 (7 ms)
[2018-02-25 18:13:31] #007 accepted (141248/59+17605) diff 400015 (29 ms)
[2018-02-25 18:13:31] #009 accepted (141249/59+17605) diff 400015 (7 ms)
[2018-02-25 18:13:31] #018 accepted (141250/59+17605) diff 400015 (10 ms)
[2018-02-25 18:13:32] #015 accepted (141251/59+17605) diff 400015 (14 ms)
[2018-02-25 18:13:32] #018 accepted (141252/59+17605) diff 400015 (7 ms)
[2018-02-25 18:13:32] #006 accepted (141253/59+17605) diff 400015 (7 ms)
```

Also here is workers.json
```
{
    "hashrate": {
        "total": [
            893.36,
            972.7,
            947.14,
            962.89,
            652.96
        ]
    },
    "workers": [
        [
            "49F............",
            "10.0.0.1",
            4776,
            141034,
            59,
            17605,
            56415715510,
            1519582332814,
            893.36,
            972.7,
            947.14,
            962.89,
            652.95
        ]
    ]
```
