It is rare for a Key Slot to be damaged, but some weeks ago the Western Digital My Passport Ultra which i use to backup Photos cannot be accessed because of damage Key Slot. A sign of a damage Key Slot is obviously the failure to access the drive even with correct passphrase.
Like many people, i forgot to make a backup of the header. I was so close to losing all the important photos, but I was still very lucky that after countless attempts of login i am able to regain access to it. Once i got the access, the first thing i did was to add another Key Slot so that if one Key Slot has been damaged there is a chance for the other Key Slot to work.
Here’s for your references:
The drive was
/dev/sdb2 and i added a new Key Slot with:
# sudo cryptsetup luksAddKey --key-slot 3 /dev/sdb1
# sudo cryptsetup luksAddKey --key-slot 3 /dev/sdb2
and then make a backup of LUKS header
# sudo cryptsetup luksHeaderBackup /dev/sdb1 --header-backup-file /home/bamf/Giri/LUKS/WD-My-Passport-Ultra-1TB-giri-sdb1
# sudo cryptsetup luksHeaderBackup /dev/sdb2 --header-backup-file /home/bamf/Giri/LUKS/WD-My-Passport-Ultra-1TB-giri-sdb2