It's actually a bug in GTK+.This is worked-around in the Deja Dup 22.x stable series. I recommend Debian update to 22.1.
GTK+ bug: https://bugzilla.gnome.org/show_bug.cgi?id=670018 Upstream Deja Dup bug: https://bugs.launchpad.net/deja-dup/+bug/929128 -mt -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
