Are you certain that the report was generated from a task and not from another action?
To verify, check if the report contains the field inputs.source. If it does, does it indicate "task"? This would confirm that the report originated from a task.
If the report was indeed created from a task, the task document should still exist in CouchDB, even though it gets purged from the user’s device 60 days after completion. The deletion from the device shouldn’t affect CouchDB’s records.
You might also want to double-check how you’re retrieving the task UUID and where exactly you’re looking for it. Could you share more details on your approach?
This related discussion might help: