@Collin129
While you are trying to find out how this happened, I would change your check-in time from flexible to a window: 5pm-11pm (or whatever you want) and see if this makes any difference
I see you use Instant Book? There used to be a problem with that as the pre-booking message (if Host used one) used to say the guest should message the Host as to when they will check in. Airbnb has since changed the wording that appears, but may not have changed the functionality that allowed guests to choose a check-in time in the App: