I can't find anywhere in Apple's guidelines what the behavior of Face ID should be in the following scenario:
- I enter valid credentials
- I enable Face ID
- I use Face ID to log in (for some period)
- I return to the login screen and disable Face ID
- I reenable Face ID
As a convenience having 5 use the credentials supplied in 1 makes sense (doing otherwise would be frustrating), but what if between 4 and 5 I enter new credentials (e.g. I've changed my password or I need to use a different e-mail address). In that case having 5 use the credentials supplied in 1 no longer makes sense.