Suddenly cannot unlock bitlocker USB drive

[CDR0224]

Yesterday I was still using it and today it won't unlock. It seems to mount and asks for the password, but then it says

An error occurred while accessing '4TB USB', the system responded: The requested operation has failed: Error mounting /dev/dm-1 at /media/carlo/4TB USB: wrong fs type, bad option, bad superblock on /dev/mapper/bitlk-42951c9d-e3d4-4b96-85c6-72af439ee285, missing codepage or helper program, or other error
​

It mounts without errors on Windows.

Strangely, in Dolphin it appears unmounted and in Partition Manager it appears mounted ... but I can't access it.

[CDR0224]

Even stranger ... Just to check that it really doesn't have a problem, I just plugged it back in to the Windows laptop where it automatically mounted and unlocked as usual. Ejected it and connected to the Kubuntu laptop again and now it works ...