Urbackupclientbackend does not remove dattobd snapshot if the daemon gets stopped in the middle of a backup

I’m using the urbackclient on my laptop (debian buster), and urbackup uses dattobd to get snapshots of the filesystem.
In general that works beautifully. But I had to notice, that urbackupclientbackend doesn’t remove the snapshots if the daemon gets stopped (on the command line or by shutting the computer down). That led to that I’ve run out of space since my root filesystem was filled with /.datto_3d41c… and /.overlay_2fefd0… files.
there were no message in urbackup.log besides:
“WARNING: Shutting down (Signal 15)”