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User table has type null

Hello,
The type of the user table in my data type tab is empty. And when I try to set it back to User I can’t type anything. at the top it mentions “fields for type null”
Has anyone experienced this?
I can’t see which users have registered, because in the app data the type user does not come up.
Somehow, existing users can log in but I can’t create any more users.
Any idea how this happened ? and how I can fix this?