Asus PRIME X299-DELUXE sometimes change the Boot in the BIOS. Why?

[FoxAdriano]

Hi, I have a computer that was assembled just over a year ago with the Asus PRIME X299-DELUXE motherboard and Intel i9 7940X processor. The PC is working very well but sometimes I get problems with the Boot in the Bios. It has happened 3 times in a year, when I turn it on, it freezes on a black screen telling me that it can't find the right Boot and that I have to go to the BIOS to fix it.

In fact in the BIOS I see that the various Boot are all different than those I had put.

So I have to manually put the right Boot and then the PC turns on regularly.

3 times in a year are not many, but I would like to understand why this happens to me.

Thanks for some info.