Haven't seen that happen here yet, but could be unnoticed, because the machine is only being monitored remotely.
One other thing we have noticed is that while rendering, some of the cards will intermittently be idle for a few seconds. My guess was this was being caused by the MSI-Utility. Might be the same thing as you seeing a frozen screen occasionally.
But indeed, great that this is finally working properly (this is actually the first time in 8 months that this machine can be put to real use - quite a waste, considering it was kinda hard sourcing 8 GTX 1080ti's back in the Great GPU Drought of 2017 :)