GRUB2 UEFI update

[Jošt Šuklje]

Hi,

new here and not sure yet how the bonton for asking questions here is, so
I'll get right at it.

Updated my BIOS (UEFI actually, but too use to saying BIOS so might call it
both) on my gigabyte AX370-gaming 5 from F8 to F20 (that is actually just 2
versions apart, not 12). Now my GRUB 2 keeps spitting out error 15 whenever
I want to load up.

I have a bit of a strange, because I want to run Grub that way; namely:

SDA is my SSD with both windows (SDA4 [NTFS]) and linux /root (SDA6
[BTRFS]), /home (SDA8 [BTRFS]), /boot (SDA5 [ext4]) on it. It also houses
windows loader (SDA3 [NTFS]), swap (SDA7).

SDB is my HDD where I keep most of my data stored (SDB5 [EXT4]) and (SDB6
[NTFS]). As well as (SDB1) With the BOOT.EFI partition on it

Any idea what could cause a BIOS update to wreck my GRUB?
Sorry if the form of the question is not up to par yet.

In hope of a reply,
Axel