I run XFCE as my DE, and use xfce4-notifyd for notifications. However, I also keep most of the KDE packages installed, as I often use several KDE apps.
The recent upgrade of the plasma-workspace package (from v18.104.22.168 to v5.10.0) broke notification on my system. The cause seems to be the inclusion of the new dbus org.kde.plasma.Notifications.service file. The presence of that new file causes dbus to try to perform notifications using plasma (even though I don't have plasma running) rather than using xfce4-notifyd and so all notifications are failing / timing out.
There doesn't seem to be any fix for this other than either removing the plasma-workspace package - and half of KDE along with it, due to dependencies - or hand-editing the file to comment out its contents so that it won't get called by dbus for notifications. I chose the 2nd option for now, but neither option is really a proper fix.
Since that new org.kde.plasma.Notifications.service is what caused the breakage, I'd think that a proper fix might require some re-thinking about the use of that file, and how to make it work properly when other DE's are present and/or running.
Sorry - forgot to include the error message that DBus gives:
Jun 23 16:55:27 darosedm dbus-daemon: Activating service name='org.freedesktop.Notifications'
Jun 23 16:56:27 darosedm plasma_waitforname: org.kde.knotifications: WaitForName: Service was not registered within timeout
Jun 23 16:56:27 darosedm dbus-daemon: Activated service 'org.freedesktop.Notifications' failed: Process org.freedesktop.Notifications exited with status 1
The correct functioning looks like so:
Jun 26 12:19:31 darosedm dbus-daemon: Activating via systemd: service name='org.freedesktop.Notifications' unit='xfce4-notifyd.service'
Jun 26 12:19:31 darosedm systemd: Starting XFCE notifications service...
Jun 26 12:19:31 darosedm dbus-daemon: Successfully activated service 'org.freedesktop.Notifications'
Jun 26 12:19:31 darosedm systemd: Started XFCE notifications service.
There is a proposed fix in newer DBus where we will copy service files into /run somewhere and have this solvable per session.
Till then DBus activation with two desktops is a slighlty rubbish area and there is no good fix.
You can solve it by autostarting xfce-notifyd with your session
also you can override .service files in your ~/.local/share.
Where is this D-Bus upstream proposal for a fix? After 2 years and a half this still continues to be the same problem.