I am missing a meeting on my calendar or my calendar is double-booked. A meeting someone else put on my calendar doesn't appear.
There have been a few instances of cached shared calendars in Outlook on Windows causing the following undesired behavior: Person A will open Person B's calendar and put a meeting on Person B's calendar. When Person A views Person B's calendar the meeting is there, but it never actually appears on Person B's calendar. This can cause missed meetings or double-booking.
Turning off the caching of shared folders in Outlook on Windows seems to correct this issue.