So I have a tumbleweed transactional server.
After latest upgrade I couldn't boot up normally as grub would show only grub
rescue> prompt and this error:
"error: attempt to read or write outside of the disk 'hd0'"

I took network install dvd and used that to go into rescue shell.
I chrooted to the system and run t-u (transactional-update) bootloader.
For the first time this fixed grub so I could pick from menu, but the recent
item/snapshot couldn't be booted never the less.

An older snapshot worked, so I tried running t-u dup from the snapshot again
which resulted in grub rescue again.
This time also chrooting to the system and running t-u bootloader didn't "fix"
grub and I still got only grub rescue prompt.

So the next step was taking the network install dvd again and I managed to boot
to the upgraded/latest snapshot with "boot linux" option from dvd.

Running btrfs scrub and btrfsck from the rescue dvd showed no errors on the
disk.

When inside grub rescue I can list the partitions, I can list the /boot
directory and the files are all there, but if I try to load insmod normal
it shows that error with read/write outside of disk.

On the system my /(root partition) is mounted with compress which defaults to
compress=zlib:3 I have also other drives that are used for data storage and
those are connected to /srv and are mounted with compress=zstd

I tried to replicate the setup in a VM, since it is easier than debugging on
the server, but VM setup even with compress and running t-u bootloader didn't
result in borked grub.