I believe the problem is from flaky solder connections, these miners are plagued with them. I have found the problems tend to show up more often when cold, then when you warm them up thermal expansion can close the flaky connection enough for the miner to run. You may be able to limp along for a while, but in my experience, it is just a matter of time before it starts failing solidly and won't come up even when warm.
The same issues can cause the temperature sensor issues. Sometimes all the downstream sensors from the place where the issue is start having communication errors.
That would fit with my symptoms. I think I may have reached that point of no return today. Couldn't get it to stay hashing on all 3 boards, even with the ambient temp up in the 50F range, which is a new low for this machine.
I disabled the 2 hashboards that were reporting sensor issues and so far it's been running fine on the remaining board. I won't know if it's significantly more stable until it has a chance to run overnight, but I've accepted I will need repairs.
I see you're in the market for 17-series components, I don't suppose you offer repair services?