To troubleshoot why all-day events may not appear at the top of your Microsoft calendar, you can take the following steps:

1. Check if the time zone associated with the event is correct.
2. Check if the event is set for all-day from 12:00 a.m. to 11:59 p.m.
3. Check if the right day is selected in the date picker.
4. Remove any categories that may be associated with the event.
5. Make sure any recurrence settings are set correctly.