No idea what the people who have problems do different, but both ZEC miners (Opti and CM) are running stable. I can not really remember when one of these miners crashed (with quite some overclock and on more than a few rigs/GPUs). ETH (especially dual) and XMR are another story, at least for me. And I am talking about Windows...
I have 2 rigs with no overclocks, on both I get 1 card hanging on optiminer. Nice to get almost almost 350 sols more, but I don't need to check if CM 11.1 give problems, I know it's OK. With only 9 cards running I can't afford to leave cards hanging, so opti not working for me and I'm not the only one with this issue. Will use it if miner can run all my cards for days not hours.
As the results (hash rate) with Opti are different compared to CM, for sure it puts another type of load of the GPUs (even if the average wattage is not that different - I did not check it because I have no reason to do so). Maybe you are also hitting some limits? Many people are much too tight with their design/dimensioning, especially of PSUs, cooling and so on (I don't say YOU did it wrong
). I remember that in the past some even experienced problems just with newer releases of the same miner (especially with CM ETH dual) which delivered higher output but was also more demanding on the hardware. That's one of the reasons why I always recommend enough reserve - and it seems to be the right way.