Quick Delivery tasks and any jobs they are in sometimes vanish for no reason. No admins manually deleted them.
There is a defect in 7.1 where the NS.Scheduled purge of completed Software Portal tasks task in Task Scheduler deletes jobs and tasks that were manually created. This task runs at 2:30 AM every day.
This defect has only been observed in Software Management Solution 7.1 (Etrack 2965283). Upgrading to 7.5 or 7.6 prevents the problem from continuing. Unfortunately the deleted jobs and tasks cannot be recovered and must be recreated manually.
To confirm that the missing tasks or jobs were deleted at 2:30 AM by the defective task run the following query and specify part of the name of the job or task: