Phantom constraint

Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while saving the entity changes. See the inner exception for details. ---> Microsoft.Data.SqlClient.SqlException (0x80131904): The DELETE statement conflicted with the REFERENCE constraint "FK__appointme__patie__37A5467C". The conflict occurred in database "Clinic", table "dbo.appointments", column 'patient'. Why? Appointments are not really dependant