When viewing the calendar by month, calendar events will not load for months in between school years.  School years need to be setup to end one day before the start of the next year.
To Ensure School Years end one day before the start of the next school year we:
  1. Go to Core > Settings > School Information > Years & Terms
  2. Click Edit for the selected School Year
  3. Update the Begin School Year or End School Year date to ensure there is not a gap between School Years