Successors are Tasks set to take place after another Task. There are a few reasons why your successor may not be rescheduling following a change to a predecessor Task:
The successor is Promised, meaning that the Task has been committed to take place on those dates
The successor already has a status recorded
If your Task has a status recorded or has been promised, it will not reschedule automatically unless manually moved itself. You’ll also be prompted to input a delay reason.