Work schedule is ending when assignment is updated

We have created work patterns and shifts and assigned work schedules on assignments. Recently, we started noticing, when there is a change in the employee assignment, such as manager change, or grade step change, the work schedule just ends at midnight on that effective date. Our overtime rules are associated with the work schedules and employees are getting overtime bacause of incorrect schedule.

Has anyone faced this issue. Does anyone have a solution for this?