Is there anywhere I can look that can show who changed an over ride? I just found a bunch of class over rides missing which caused us to not get alerted.
Unfortunately, it is not possible. There’s no auditing in SCOM. However there’s a uservoice request, you can vote it:
FYI, this is now possible via SCOM 2019 UR2.
I think if the override doesn’t exist you’ve even less chance of finding out who modified it than when they are just overridden! Auditing is one of those areas which is sadly lacking.