Reading what @maycne.sonahoz says in this post about stopping Update Manager:
Can you test if app-msm_kde_notifier@autostart.service and app-pamac\x2dtray\x2dplasma@autostart.service are both in “loaded active plugged” status? An easy way to do it:
systemctl list-units --user | grep pamac
systemctl list-units --user | grep kde_notifier