I have just upgraded our site from 1.9.19 to 2.4 via intermediates as necessary. I have encountered an issue with course categories and bread crumbs but I feel that the problem may be wider than that.
In essence the following screenshots show the outward symptom.
I noticed this when courses in English failed to load when I clicked on the course link shown above. Got an error about missing table or similar (sorry did not get screenshot and error no longer appears). I moved the courses into the 'Science' category then back out to 'top' and now the courses do load fine but the bread crumbs still don't work.
Yesterday after completing the upgrade to 2.4 I notice that I had foreign key errors e.g.
Any suggestions appreciated.