After spending half the day crashing the card and resetting the system, it seems that the hang is caused when GPU-Z tries to read the BIOS of the slave card.
GPU-Z asks the driver "is this card in ULPS?" and if yes, then skips BIOS reading. But the AMD driver tells me "no no you can go ahead", and boom system crashed.
Now trying to figure out how to work around this. Not having high hopes. I might just disable BIOS reading completely for all slave cards.
Originally Posted by Plug
This does not happen with AIDA64
aida64 never touches the slave bios when ulps is enabled