Shutdown is slow, always waiting 2 minutes for gvfsd-fuse to terminate

My desktop is using OpenSuse 15.1 with latest updates, systemd 234-lp151.26.16.1, gvfs 1.34.2.1-lp151.6.3.1. Since a while (I cannot remember exactly when it started) a system shutdown takes at least 2 minutes to complete. When I hit ESC at the splash screen, I see systemd is waiting for a User Manager job to finish and, after some digging, I figured out that it is this process: /usr/lib/gvfs/gvfsd-fuse /run/user/1000/gvfs -f -o big_writes I did some research and discovered that this is automatically started by programs like Firefox and Thunderbird (and others). I also verified that: - If I boot and don't use such programs, the shutdown is fast; - If I logout and use the console to kill those user processes, the shutdown is fast; - Other user accounts are affected too, only if they use the mentioned programs. I configured systemd with: KillUserProcesses=yes, but it does not help as it seems those processes still take 2 minutes to be terminate after the logout. Furthermore, on the same machine I can also boot Ubuntu-mate (18.04 LTS) from a separate SSD and it shows the same symptoms. How do I figure out what's causing the 2 minutes delay ? Edit: perhaps it's worth mentioning that once I logout, I cannot log back in again because I get a dialog "Could not sync with Dbus". I need to do a ctrl-Backspace to reset X first.