User Account Keeps Being Set to Login Active = No

You flip Bob back to Login Active = Yes.

Bob tries to login the next day.

Bob will not be able to login.

Why?

Almost certainly because you have the following feature enabled and the user did not sign in before approximately midnight of the day you set their account back to Login Active = Yes.

Admin > Site Settings page:

The system runs that check at approximately midnight each night. The time varies, but we recommend telling Bob that he must login before midnight.