My Ubuntu Software doesn't show installed programs or available programs any more

Solution 1:

Since this is a known bug which Canonical must fix, may I offer an alternative until then? https://help.ubuntu.com/stable/ubuntu-help/addremove-install-synaptic.html.en describes the Synaptic Package Manager which is described in the link above as more powerful and can do some software management tasks which Ubuntu Software can't.

Solution 2:

You can fix some problems with:

pkill gnome-software
sudo rm -r /var/cache/app-info
sudo appstreamcli refresh --force --verbose

These lines solved my problems :-)

Found the above commands in this answer to Why is Ubuntu Software Center dropping previously provided applications? by Terrance.