LR Classic crashing on Import

[Frodo]

As the title says, I'm finding that LR Classic is hanging up and then crashing when I click the "Import" dialog button or access import through menus.  If I reset preferences (Shift+alt when starting LR in Windows 10), the problem goes away, but then I have to reload my preferences.  And then a fortnight or so later, the problem repeats itself.

Any suggestions?

Thanks, Bob