I think I do have a similar issue:
$ snap list Name Version Rev Developer Notes core 16-2.26.9 2381 canonical -
$ sudo snap remove core error: cannot remove "core": snap "core" is not removable
$ df ... /dev/loop1 82432 82432 0 100% /snap/core/2381 ...
$ sudo umount /snap/core/2381
$ sudo snap remove core core removed
Maybe this helps?
I think I do have a similar issue:
$ snap list
Name Version Rev Developer Notes
core 16-2.26.9 2381 canonical -
$ sudo snap remove core
error: cannot remove "core": snap "core" is not removable
$ df
...
/dev/loop1 82432 82432 0 100% /snap/core/2381
...
$ sudo umount /snap/core/2381
$ sudo snap remove core
core removed
Maybe this helps?