If you have stuff in lost and found then you have a file system error. From rescue disk run fsck on the root partition. Note lost files may not be complete or continues so if binary it is unlikely to be able to recover such files. So full restore is questionable. Maybe you are lucky maybe not
Also from rescue disk run smartctl pointing to the drive in question.
If running BTRFS maybe just maybe you can boot to an earlier snapshot
Still unknown how you boot. Do you have a older BIOS or the newer UEFI. If UEFI then it still maybe legacy MBR boot dependent on how you installed.
I believe am lucky, because all the lost+found directories are empty.
Then I explored all the /boot/ directories and found that only the sdc4’s /boot/grub/ does not contain subdirectories as another ones.
Then as SU I copied with all the subfolders /boot/grub2/ from sdc1 to sdc4 as /boot/grub/
After restart the PC it boots correctly, without grub rescue> at all, but there is not the newest installed Linux as an option in grub-list.
At least I copied the file grub.cfg from sdb to sdc4, because it contains all the available Linuxes.
After restart of the PC all the Linuxes are in sdc4’s grub-list for start.
I have an older BIOS and probably I have MBR-boot …
Thank you.