LattePanda Mu BIOS Boot Priorities reset themselves after a while

I am working with a LattePanda Mu Lite Carrier, which came with Windows 11 pre-installed, and I have installed Ubuntu 24.04 on an SSD in the M.2 PCI-e NVME slot. I am still using the BIOS version it came pre-installed with: LP-BS-S70NC1R200-SR-A.

I can boot into either OS, no problem, but I want Ubuntu to be the default boot option. I can set Ubuntu first in the BIOS Boot Option Priorities, and that will keep Ubuntu as the default boot option for a little while, even after complete power loss (i.e. unplugging the LattePanda completely), but after a little while (on the order of a couple days), the default boot option will set itself back to being Windows 11. 

I have an RTC battery installed, I have disabled Secure Boot, and I have disabled Windows Fast Startup, but none of those commonly suggested fixes has fixed my issue permanently. 

Has anyone else had this problem with the LattePanda Mu? Does anyone know a solution?