Invalid nonce; is miner not compatible with NiceHash?
Environment:
1 xmrig-proxy (master branch) - simple mode
22 xmrig workers version 5.6.0 - nicehash enabled
Mining randomx to nicehash.

Problem:
From time to time, the proxy is reporting Invalid nonce.
While workers have no error when this error occurred.
![image](https://user-images.githubusercontent.com/3666089/75128619-f8db6b00-56ff-11ea-9580-dc59be57cac1.png)
