I have 2 Vega 64 LC - completly hang pc when gaming when Crossfire or Single (on one card with problem).
I did some tests and now i can say that one of the card have trouble with factory gpu clock on any power profile and any drivers (Total War Attila, Rome 2, Thrones of Britania, Witcher 3 etc). I changed GPU freq. from 1750 to 1740 (in Afrerburner i search optimal freq, after found save it permamently by power table editing in OverdriveNTool) and no hangs after that.
No it not helped, need to lower power limit for second gpu - minus 30% (yes, second bios switch not helped at all). I will RMA this card, faulty 100 %.
PSU 1 KWt - each card with seperate 8 pin cables (4 total, not combined). 12v line not going lower 12.00v under full load (in my case - 860 W/h).