I'll do the same.
I've just re-exported the calendar from the old system via PC O2010, re-imported it into O365 via PC O2010, then re-exported it to a PST again via PC2010, deleted it the entried on O365, and then re-imported from the pst back onto O365 via PC O2010, and still the same.
Can see the imported files on the PC O2010, can see new entries added on the Mac on both the Mac and PC, Mac can't see any of the imported events.
My thinking was that to import and export, then re-import it might change the mapping withing the PST, and fix it.
I can also see on EAC when the public folder says 1648 items, and when deleted you can see 0 items, then re-import it back to 1648, so O365/EAC are seeing it.