Fatal error while backing up /var with snap/lxd

I have this error while making a backup:

! Error when processing “snap/lxd/common/ns/shmounts”: invalid argument
I am trying to back up /var from my server, and this is showing up.
How can I get rid of this fatal error?
Trying to play with .kopiaignore, but the documentation is not there or clear at all.

Thanks for your help,