I'm sure you've tried it, as you appear more techy than me! But since I don't see it listed....
Did you eliminate SSD failure from the equation as well? I'd try a SINGLE SSD, and start with an install from scratch. I'd try that first, to test for RAID controller failure while you're at it.
Wish i had more ideas for you, sorry 😕 After all the horror stories I've seen, I'm dreading ever having to deal with ASUS customer service >.<