When trying to migrate a Calendar from Exchange to O365, every item fails with the error:
"The operation failed because an unexpected error occurred. (Result Code: 0x81070906)"
The Calendar itself can migrate, but none of the items migrate. Using a .PST file to migrate produces the same error.
One thing noticed is that there is a folder in the Exchange Calendar called 'TimeProfile'. As SharePoint calendars do not allow folders, if you select all Calendar items and unselect 'TimeProfile', the items are finally able to be copied.