Applications emitting desktop notifications freeze for some time

Solution 1:

It turns out I somehow broke the autostart of the notification implementation. In Unity's case that's /usr/lib/x86_64-linux-gnu/notify-osd. That thing should be running. If it's not, the applications freeze.

So the solution is to add that executable to the startup applications.

There is some useful additional information here: https://wiki.archlinux.org/index.php/Desktop_notifications

Solution 2:

I understand this is quite an old thread. But you, My Good Sir, just helped me fix the same issue after I had tried KDE Plasma Desktop(the kde-plasma-desktop package) on Ubuntu MATE 20.04. Somehow during the process, it had removed the notify-osd package. After seeing your answer, I ran:

sudo apt install notify-osd

After it got installed, I restarted the system…and voilà! It's fixed now! Thank you so so much!