Entries stuck in SM13 queue in 'INIT' status

I have been trying to figure out why some entries are stuck in SM13 with status 'init'... user made changes to delivery using VL02N and it resulted in entries stuck in SM13 in 'INIT' status for more than 20 hours..After a while the update task is completed. This is happening randomly and it is difficult to figure out the action taken that caused this issue.

Any ideas?