When you see this error message in your reports:
It could mean some other Facebook application that has been authorized with the same User token might be exhausting the limit for the number of requests that can be made in an hour window to Facebook’s API. Subsequently, we can’t hold enough of this limit before getting into a throttling error.
It appears we cannot do much about syncing the data when this happens. You will need to check your Facebook account and all other integrations to see where their limit might be spent before we can successfully start syncing data again (or simply wait until we get enough quota from Facebook at some point).
Currently, if a client is affected by this problem, you will see an error in the interface that says "Facebook User request limit reached. We are getting throttled." like the one above.