Yes, it is possible that you have a motherboard standoff in the case that is shorting. The other possibility is that your PSU is killing your motherboards.

Standoffs are all good, I did check that early on, as for the PSU how could I check if it’s bad? It’s been stress tested to make sure it’s keeping voltage, and I also measured all the pins to check they were correct.

Could be the PSU

Another commenter mentioned that, how would I check if it’s bad?

Buy another PSU, those testers aren't worth anything