How many rejected shares one got to be worried about? I'm using NBminer to mine Ethereum on nicehash pool so far I got 78 accepted shares and 9 rejected shares, should I be worried? Phoenix miner latest upgrade lower my hashrate that's why I switch to NBminer, seem more stable, I don't overclocked my gpu and it's temp is below 58°C
acceptable rejected shares 1-3% over that you should reconfig the miner or gpu clock setting, maybe to much memory overclock, temp under 70C still stable on many gpus
check vram temp, and the riser or something wrong with os/your internet most likely this wont happen but just check it anyway..