Since upgrading from 2015 to 365 we have had some users (about 5 out of 100) get either the above error message or have long synch times which prevents them from tracking or set regarding new email. If we let the synch go it can take several hours for it to finish only for it to have long synch times later in the day.
For the error, we created a custom form that allowed us to search for CRM link states that were either 1, 3 or 4. On two of the users computers we were able to find items that were in such a link state and un-track them but that only seemed to help with the failed promotion error. Those two users are now seeing long synch times yet again.
For the other three users we could not find anything with a link state of 1, 3 or 4.
Looking at the trace logs is not all that revealing. I have those trace logs if someone would like to look at them I can email them to you (as I can't figure out a way to add them here.)
Thanks!