20.04 recent upgrade : caja fails to open

From menu there is no response.

From commandline

 caja: symbol lookup error: caja: undefined symbol: mate_desktop_thumbnail_scale_down_pixbuf

This error also occurs when you attempts to upgrade 18.04 with the Mate PPA for 1.24. Silly me wanted a newer version of Atril, because some PDF files don't render correctly. Where are Snap/Flatpack when you need them?!

Trying to back out of the upgrade by removing the PPA and re-updating does not solve the problem. You can install Nautilus to get a file manager to use, but it's not as smooth to use as Caja.

If I decide to try it, I'll see what happens with a 18.04->20.04.1 dist-upgrade next week. Clean installs of 20.04 don't show this problem.