Parent deck case mismatch causes errors

Originally posted by @IMBK01:

The issue is that the parent deck name has been used inconsistently, which older Anki clients (and currently AnkiWeb) don’t support. Eg, you have a deck called Parent, but have then used “parent::child” instead of “Parent::child”. Normally Anki should automatically ensure the case matches for you when you add a deck - which client did you use to add the decks?

If you rename the decks using the latest Anki version so they’re consistent, you should be able to force a full sync to AnkiWeb to fix the issue.