Dear Francesco, I'm a member of the new upstream maintainer team.
I assume this is reported at upstream https://github.com/bit-team/backintime/issues/1003 and also fixed there https://github.com/bit-team/backintime/pull/1380 Please try to reproduce that problem with the current upstream version.If you can still reproduce it please open an Issue at upstream and link it here.
I suggest to close that Debian bug report because it seems not distro specific.
Kind Christian Buhtz
