When you create an Auto Task template, you can choose when the task begins ("Schedule for") and you can also set a time frame for the completion of the task ("Can start from" and "Must finish before").
These tasks are linked to the schedule of the a reservation, and therefore changes in the reservation's schedule may cause changes in the tasks' status. For example, you made change to the check-out time of a reservation, tasks with a "Confirmed" status linked to that reservation's check-out schedule, will revert to a "Pending" status.
This behavior is by design, and helps ensuring that the assignee of a task is aware of the change in the schedule. The tasks will be re-confirmed when the assignee accepts the task via the Guesty mobile app