21.04 MATE up to date today.
My MATE desktop comes up without panels. Each time I have to issue
$ mate-panel reset 
This restores the panel but also displays the message
Unable to open desktop file screensaver.toggle.desktop for panel launcher
Unable to open desktop file timer.desktop for panel launcher
Unable to open desktop file display.flip.desktop for panel launcher
Unable to open desktop file /usr/share/applications/google-chrome.desktop for panel launcher: No such file or directory
Unable to open desktop file /usr/share/mate/applications/spotify.desktop for panel launcher: No such file or directory
....
Unable to open desktop file caja-1.desktop for panel launcher
Unable to open desktop file caja-2.desktop for panel launcher
However from this list I can find these files :
 /usr/share/**mate**/applications/spotify.desktop 
./.local/share/applications/timer.desktop
The only panel references in the journal are about successful activation.
 
    