error: failed to enable crypto I/O mode for container /dev/rdisk3: Invalid argument

Before you tell me that there is a problem with my physical device, let me assure you -- there isn't!

This problem happened after upgrade to BigSur, and it was working just before that. Also, there is another partition on the drive, and it works just fine.

Reboot after the upgrade, and my external APFS (case sensitive, encrypted) fails to mount. I try to run First Aid, and I get "operation canceled" right after "unlocking disk"

so I run

sudo fsck_apfs /dev/rdisk3s1

in the terminal, and I get

** Checking the container superblock.
** Checking the space manager.
** Checking the space manager free queue trees.
** Checking the object map.
error: failed to enable crypto I/O mode for container /dev/rdisk3: Invalid argument

Searching the web for this error doesn't yield much. There are support tickets with apple describing similar problem pointing to a bug in the BigSur, but no resolution yet.

if you have ideas how to fix that please post. If you have a similar problem, perhaps just click "I have the same problem", unless you have some useful clarification, that may help find a solution. And once again, if your opinion is that it is a hardware problem, please keep it to yourself. Suggesting to remove and re-create the partition is also not helpful.