Considerations for Closing and Reopening Tasks in Lightning Experience | Salesforce
Suppose that you’ve created a validation rule for tasks; for example, you require users to enter a comment before closing a task. If you’ve set up more than one Closed status for tasks, users must choose a status when they reopen or close a task. If you’ve set up more than one Open status for tasks and a user reopens a task, Lightning Experience remembers the last Open status.
|Available in Lightning Experience in: Professional, Enterprise, Performance, Unlimited, and Developer Editions|