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2. I have a few rigs on v11.5 and they are working for days until I restart miner to perform some new tests, but I always use non-overclocked cards and default bioses, I have to do it to exclude everything except miner in case of any problems. When you use miner on overclocked/unstable rig you cannot be sure that the reason of the problems is the miner, but of course you will blame it
Try to reduce "-ethi" value, if it does not help you can use the version that works fine for you.
I've had this miner running for over a month before till I shut it down on purpose for some maintenance, and that was with modded/undervolted cards. If you have instability the miner is probably not the culprit. Once in a while I will see a card report a hashrate a few Mh/s below normal but it's very brief and will only appear on one line of reporting. If I hit 's' after or wait for the next report it's already back to normal.
I think most people just don't do proper stability testing after they start messing with clocks/volts/timings.