Hi ,
This type of error usually occurs due to a problematic object in the Revit model. It is usually a single object but can sometimes be caused by multiple objects. Unfortunately, there isn't an easy way to find the exact object that is causing the problem other than hiding any objects that were not present during your last successful sync, then unhiding each one individually and attempting to sync. Once you encounter this error again, that will let you know that the most recently unhidden object is the one causing the problems. By deleting and recreating the object, that should fix the issue.
Best,
Raghib