A Basic multi-card note cannot be changed to a Cloze type

All target card slots map to Nothing with no choice possible. No Empty cards. How could that happen?

Anki 2.1.22, 2.1.26, 2.1.28.

Anki currently only supports mapping one of the templates to the cloze template. I believe there’s an add-on that extends this.

But that note can’t be mapped at all, not even a single card.

Works for me - if issues persist after ruling out add-ons, please provide a reproducible example.