I have experienced the exactly the same problem for the past few weeks only. Only (temporary) solution has been to delete the tree on Ancestry and upload a fresh one from FTM2. However, after a couple of changes to the FTM2 data, the sync issue re-appears.
How can one do a complete re-install of the latest version on a mac. I have the original discs but don't want to go through having to then upgrade them with updates. Is there somewhere I can access a downloadable copy of the latest version?