I have updated to 1.6.6 on this machine, but I also ran the log to see if we could tell anything about the hash rate drop. This is what it shows in the log (doesn't seem to show anything to me):
unfortunately i dont have a full rig of vegas, i have only one card im testing on, but what i noticed is that if i start mining, and use a browser for a few minutes the hashrate on cnv7 drops and never recovers back to the original one.
Also hash is lower while im connected to this machine on teamviewer/anydesk.
Maybe someone with much more experience with Vega rigs can help you.

This machine is run headless with the iGPU used for display purposes and teamviewer. This happens when I am not connected to it. You are more than welcome to test stuff with me on this rig if you would want. I also wonder if I setup up the watch dog setting, will it pretty much do a full reset of the miner just like me restarting it (rerun the startupscript and everything)?