I found someone talking about UEFI and they was talking about it in windows 8. According to them you had to have secure boot turned on or at times it would revert back to legacy.
Not true. Secure Boot does need UEFI, but UEFI works fine without using Secure Boot.
It looks like for some reason it is loosing the drive during boot, and it checks very early in the process. If the drive is slow to start it might be missed. Can you change the SATA port it is on for testing?
You might also try turning off the
fast startup for a while to test. Any problems with the drive itself?