After a recent update, some of the Mate panel icons changed to a red circle/slash. When clicked, the panel apps those icons are associated with, launch without any problem. I have tried resetting the panels via:
and then reconfiguring the panels, but the icons are still broken.
No, the theme was not changed. The only thing that changed was whatever changes the updates made to the system. Funny thing is, the icon displayed in the Launcher Property editor displays as it should. At the moment, I am unable to access the computer on which this problem has manifested itself, so I can't click the icon in the editor to see if it really points where it should. Thanks for the suggestion, will get back with results when I can access the computer.