Anki made a change a while ago where using their newer scheduler also changes their deck format. This made decks using that scheduler incompatible with Kitsun’s import. I think this might be the issue you are currently running into.
I believe there was an option to tell anki to use the old format, after which you would be able to export the deck and try again.
Another option might be to export the deck from anki as tsv/csv or other supported import formats. The only downside to those imports is that it does not import media files, so that might not suit your deck.