Partition on eMMC disappears as boot option

I’ve 20 Rock PI X and installed Windows 10 IoT Enterprise last week, which works great on it, also after switching off or restarting it several times.
But from now on, the PI no longer boots from the Windows partition on the eMMC, but from the EFI partition.
From this point on, the Windows partition is no longer visible and selectable in the UEFI setup.
However, it is still present in another partition program.
This has now already happened with 7 of the 20 PIs.

Thanks for any help.

Do you have RTC battery installed?