Eagle... one workaround when I see all of the Shared Calendars stuck synchronizing...
I go to the Calendar and i quickly toggle on and then off several of the shared calendars. It seems to reset some switch, it doesn't totally make sense, but it seems to work. I also thinned out the number of shared calendars, only keeping the ones I frequently access. I don't know if that is an option for you. The Mac Outlook to Exchange problems are increasing.