Ah ok. I'm trying to figure out if you have successfully run all 3 GPUs in 100% before the crashing? 850W sounds a little weak for 3 Turbo (factory overclocked) GPUs... Most PSUs usually don't perform with stability near their max load. Trying to eliminate the usual caveats here...
The PSU is at 92% efficiency, i saw a lot of forumers with this cofig and since i got the started for a little while i dont think here is the issue.
Make sure when you start your 2nd and 3rd miner that in the drop down menu the right gpu is selected.
They are