msi z790 carbon wifi

Randomly, only during Macrium Reflect automated backups, my PC loses the SSD containing C: and crashes. The next morning I find it at the BIOS screen because the entire SSD is missing until I do a hard power reset. BIOS shows other SSDs, but no Samsung 990 Pro which contains C:. Reset button...

Hello All, I'm a veteran builder but this problem has me completely stumped. This is a ground-up, new build, my components list is below. After assembling the PC, there was no POST, no fans no clicks, the only sign of life was the CMOS, and SMART buttons were lit on the back of the MB. I went...