It seems that in your code, the only (relevant?) use of Time::Piece is in PM::CB::Communication for the timestamp. But you only use Time::Piece there to parse the incoming create time and convert it to some other string. This should be fairly safe, but maybe mod:://Time::Piece runs afoul of setting/resetting timezones or locale data between threads.

Does the problem go away if you switch from Time::Piece to POSIX::strftime and manually convert the string (resp. replace the string with a hardcoded dummy)?

        if (@nodes) {
            $self->{to_gui}->enqueue(
                [private => '<pm-cb-g>',
                            'Time::Piece'->strptime($_->{createtime},
                                                    '%Y%m%d%H%M%S')
                                ->strftime('%Y-%m-%d %H:%M:%S'),
                            "New node: [id://$_->{node_id}|"
                                . $_->textContent =~ s/\n//r
                                . '] by [id://'
                                . "$_->{author_user}|$_->{authortitle}
+]",
                            NOT_DELETABLE])
                for grep ! exists $nodes{ $_->{node_id} }, reverse @no
+des;
            @nodes{ map $_->{node_id}, @nodes} = ();
        }
[download]

Alternatively, you can maybe try to run your code with $ENV{LANG}='C' or $ENV{LC_TIME}='C', or whatever is used to reset the information there... If that "helps", this points towards a locale handling bug/conflict between threads and Time::Piece, but that's where my ideas end.