When I restart plasma it logs the following:
[ 1336.013117] systemd[973]: Stopping KDE Plasma Workspace...
...
[ 1337.031215] plasmashell[5782]: Entry is not valid "org.kde.kontact.desktop" 0x55bc52fa6bb0
[ 1337.031264] plasmashell[5782]: Entry is not valid "org.kde.discover.desktop" 0x55bc52fa6bb0
[ 1337.031311] plasmashell[5782]: Entry is not valid "org.kde.kontact.desktop" 0x55bc52fa6bb0
[ 1337.031353] plasmashell[5782]: Entry is not valid "org.kde.discover.desktop" 0x55bc52fa6bb0
Why does it think the entries are invalid? The mentioned desktop files do not exist in either /usr/share/applications/ or ~/.local/share/applications.