The route to fetch open tasks doesn't allow unassigned tasks to be filtered.
Solution
Update the route to get all unassigned tasks by filtering, with "unassigned" as person ID.
Example: https://example.com/api/data/tasks/open-tasks?page=1&person_id=unassigned
Problem
Solution
Example:
https://example.com/api/data/tasks/open-tasks?page=1&person_id=unassigned