Thank you, @ajd
Yes, in the meantime I narrowed my problem down to the identical issue you had.
And same thing, the fix looked ‘simple’ for someone who knows their way around databases, but is beyond my capabilities!
Given my site is only a small one (20 or so digital products), I ‘fixed’ it in a couple of hours, by essentially starting again, but it wasn’t a total rebuild…
After backing up and restoring to another site, I reset WordPress (careful…you lose everything, including customizations! but the database tables are all reset) Then I re-imported all my products, categories and media from the back-up site.
Then I manually re-created all my theme customizations by referring to my backup site set up.
Super-clumsy layman’s work-around, but for me with such a small site, probably a similar time-frame to finding/hiring/briefing/paying a developer.
Might help someone out there…