AOL Calendar events that mysteriously vanish may just be hidden from view in unselected calendars. Events in your AOL Calendar only appear if the specific calendar where they were created is selected. Make sure you've selected all of your calendars to see all of your events.
1. Click the Calendar icon 
in AOL Mail | click Calendar full view.
2. Click My Calendars and Others to expand if they are collapsed.
3. Make sure you have the check mark in front of each calendar.
After you complete these steps, all of your calendars are selected and all events should be visible. If you don't see the event you're looking for, you will have to create it again.