My A900 had issues mining at nicehash. It would go good for 12-48hours or so and then 1 of the mining units in it would stop and go to 0mhs in the dashboard. The other would still show ~450mhs but it would show 0 activity in the live graph and my nicehash address would show there wasn't any mining. I'd have to go the the miner and restart it (and actually before restarting the blue light was flashing like when it starts up). This happened a handful of times

I switched to only mining at a x11 dash pool and its been fine since!