It just happens at random, not reason could be idling, gaming, browsing the web. A fresh install stops it for about a day but it comes back just as hard. Restarting can stop it for an hour or so. Or make it 10x worse. There's no rhyme or reason to it.
One thing I did notice is when it does crash AMD settings Also crashes and you need to start it twice to get it working again. But as AMD settings wasn't present before crimson (driver updates didn't help) it is not the issue.
My friend with a similar card 7970 by another brand and 2 years newer rebuilt his entire PC thinking is was just the old motherboard / psu is still getting this problem. There's no solution. Are the cards both broken? What could be causing it?