I am using a software called DeepFreeze on two 4xvega56 mining rigs to freeze any changes in my working virgin windows/vega installation.   



The freeze state boots with a fresh windows installation, no updates whatsoever,  with the  23aug blockchain drivers manually installed by device manager, and no regedit mods.  A virgin installation.  It always boots in this state.



After booting, I have scripts that apply the regedit powerplay mods, reboots the drivers using CRU.exe, uses devcon.exe to disable/enable the cards a few times in a row, and finally applies a custom overdriventool.exe profile , followed by xmr-stack-amd.exe. I never had a hashrate drop in one week of running, tested across many reboots.  Always static performance.  until now....   



One of the rigs, after running perfectly for one week without hashrate drops, its now beginning to drop the hashrate after a few hours.  Again, windows installation is frozen to the same state as one week ago. No updates, no driver changes.   This hashrate drop purely caused by another variable affecting the cards.  The other twin rig, has no problems whatsoever.

I have tried without success to:
- Decrease core/mem speed
- Increase Fan RPM by a lot


My latest try was to increase the voltages, which were already on the high side (0.980v).



If someone has a clue as to why 4 perfectly running vegas started to hashrate drop in a frozen windows installation, please share!