The lock file could not be opened for exclusive access by LibreOffice, due to missing permission to create a lock file on that location or lack of free disk space.
I haven't a lot of free space - 10GB but that should be enough to open a 2 row test file.
I was trying a simple test before recommending Base to an inexpert user, at the moment I can't do so, unless there is a very simple way to fix this. I've had this sort of thing happen with other Snaps, so I'm inclined to stick to debs where possible in future.