Deleted Task items not available in Recycle bins and Audit logs

Question

Few tasks got deleted from a task list in a SPO site collection.

I had already subscribed for alerts on deletion and I got automated email notifications when they got deleted.

But unfortunately the deleted items are not available in both recycle bins.

Audit logs also doesn't have any trace of those deletions.

In the automated email alerts I received, the username who deleted the item is displayed as "unknown"

I would like to find out who deleted those items and why are they not available in recycle bin?

Please Note: Other deleted items are available in recycle bin and Audit logs.

Answer 1

It was the "Auto Cleanup Job" which deleted tasks which were past 60 days.

I thought Auto Cleanup Job would delete only the workflow history but not happy that even workflow tasks getting deleted.

Now need to find a workaround to preserve the workflow tasks for audit purpose :(