I've a strange Problem now...was running 2 Vega56@64 Air Bios but was unable to get them stable so i was running with Bios Switch in Position 2(Should still be 56 Bios also if 64 is on Position 1 right?) at 3700H/s with CastXmr

Now i flashed both back to original 56 Bios and iam able to get ~1970H/s with both Cards if just 1 Card is plugged. If i plug in the second Card and start the miner i get much artefacts and the pc crashes. Ive an old Z77Pro 3 Board with 2 PCI-E Slots and it seems that its always the Card in 2nd Slot which crashes the System. Any ideas why its crashing now and not before with Bios Position 2?