Just out of curiosity: Do you remember if you tried updating manually by checking for add-on updates? (under Tools → Add-ons). I’ve seen a few reports of add-on update issues recently, so I’m starting to wonder if this is a general issue. In this case for instance, Review Heatmap should have definitely been updated (you are using the AnkiWeb build of the add-on, and normally Anki should have updated your add-ons as you upgraded to 23.x).