This issue can be caused by iOS devices using the native mail app to edit a calendar appointment.
To resolve:
- Navigate to Settings on the iOS device.
- Select Apps.
- Select Mail.
- Select Mail Accounts.
- Select the BGSU account.
- Toggle the Mail and Calendar sync Off.
Wait a few minutes then turn the Mail and Calendar Sync back On. Please note, it may take a while for everything to sync again.