This has been happening to me since upgrading to 2014. Running W8, now 8.1 with 32 GB and 1.
TB. It is almost always old links. I am rather sure that it is due the linked file being missing. Not sure why they are missing, Often if a link is associated with several facts, such as a public member tree with name, birth, etc., there will be a stoppage with each deleted link. It will also happen if facts are added in Ancestry, then sync, and then deleted links before the sync has finished.
It does not stop working if a fact is deleted.