Workaround:
Close and reopen Event Manger to show you a fresh view of the scheduled events, to make sure the list events shows all the scheduled events for the day.
If this fresh view of the scheduled events does not show the Change Posting Date event, then schedule the Change Posting Date event, dragging it from the Event Manager Available Events list, under System Administration>End of Day Updates events, giving it the same first priority (priority=1) or nearly first priority you had before.
IMPORTANT! Take care to not schedule the Change Posting Date event more than once per day. Only schedule a new Change Posting Date event if there clearly is not one scheduled.
There is no known reason for the Change Posting Date event or any other scheduled event becoming unscheduled, other than for a user to make the event unscheduled at some point in time. Unfortunately, changes to the event scheduling are not something logged by the application, which means there will be no record of which user unscheduled it.
ArticleNumber:
000071124