"CMOS checksum error" after BIOS reset on F2-221

[rusanovd]

Hello,

I get the message "CMOS checksum error" after resetting BIOS and this message stays on even after restoring the default settings. This message stays on for a while and usually disappears after removing the AC power for at least a couple of hours.
I've tried using the Reset button, removing the CMOS battery, shorting the + and - terminals in the battery socket, replacing the battery with a new one, but nothing has helped so far.
Around the time I started seeing these errors I noticed it was no longer possible to install any 3rd party OS to any type of HDD/USB stick on the device neither in Legacy, nor in UEFI boot mode, although it was possible before.
I've had a few exchanges with the support over email, but without success - every time a different person answered and most of the troubleshooting was around updating the InitBoot internal flash drive, instead of the actual issue. After following their advice I ended up with a new flash containing InitBoot J3355_5.12_V4.9.9, which is still something - TOS installs and runs and is probably more stable than before, but the BIOS behavior is what concerns me.
I was informed by the Support Team that my BIOS was too old and could not be upgraded, but even if this is the case I would like to try to reflash the version I have. How can I do this?

The label printed on the board says 000-F2221-FBA002-0001 and the BIOS version is 2.18.1263 (5.12 from 10/19/2018)

Screenshots and a picture of the board that connects to the HDDs are attached too.

P.S. I wrote a longer post with a more detailed description, but unfortunately in the wrong subforum and I cannot move it here. Here's a link to it:
viewtopic.php?f=21&t=2576