Ok. I returned the app to prototype state (we are still testing this version anyway), and the problem went away. I then checked the account (See screenshot). Over the whole account, there are still only seven unique users.
Do you still recommend that developers maintain different appsheet accounts depending on the status of the apps they develop? I know that in the past, if I had a paid-for app and a prototype app (essentially free) under the same account, and the paid for got blocked for some reason, this would affect the prototype app