After 40 min mining to Nanopool my reported hashrate by the pool is just 1800 mh/s, but my miners report 6600 mh/s.

the same - in Hashrate Now is hashrate only aprox 1 GPU card, not all GPUs in rig, sometime even less...

same situation.
Also many messages: Info Received response method:miner-submit JSON:{"id":48,"result":{},"error":null}