The functionality of creating and using Recurring tasks in Workfront has several rules and exceptions listed below:
1. A task will have a recurrence rule, which dictates how many Subtasks it should generate and which dates they should have. If a recurrence rule is changed after the Task creation, the existing Subtasks are destroyed and replaced with new Tasks that follow the new rule. The existing tasks are not reused because the count and dates could be totally different.
2. The exception to this is - if the Subtasks have work done on them (or are involved in a predecessor relationship). Having work causes the Subtask to be "locked", meaning it's no longer subject to it's Parent's recurrence rule. The reasoning here was to prevent a Task, that's being worked on, from being destroyed automatically by the system. Once a Subtask of a Recurring Task has work, you can consider it as no longer being part of the recurrence.
3. There is another interesting use case to consider: Assignment behaviors differ in the case where the assignment is made directly on the Parent or on the Subtasks. Since Recurring Task settings are transferred from Parent to Subtasks, when the assignment is made on the Parent, the assignment is being transferred to the Subtasks. So, if, as a result of frequency changes on the Parent, Subtasks are deleted and recreated the assignment is being made again. But in case the assignment is made on the Subtasks directly, and if you change the frequency on the Parent, the newly created Subtasks won’t have/inherit the assignment.
Find more info about Recurring Tasks here: