Broken fonts after Ubuntu upgrade to 20.04

[Ofnuts]

Eventually upgraded my Ubuntu from 19.10 to 20.04. In the process a bunch of fonts are broken:

• Display as square with hex code
  
• Seems to affect a bunch of "L" font : "URW Bookman L", "URW Palladio L", "Nimbus Sans L", "Century Schoolbook L"... while there are non-L versions
  
• Also some others (Bitstream Charter, Courier, Courier 10...)
  
• These fonts are found by the font manager (but not listed in some apps, such as LibreOffice)
  
• I don't remember installing these fonts from other sources (I usually keep the downloaded ZIP around)
  

Any idea of what is going on? And how can I reset Gimp's font catalog?