For those posting about sync issues in the past 48 hours or so, Dec 27-29, the Ancestry site has been having server issues. There are plenty of posts on the Ancestry Site Comments board about the server issue. This is a good board to check BEFORE your sync.
Set you sync to manual, and always choose when to sync.
Ancestry was offering a promotion that ended midnight Dec 29. Whenever they run a promo, the servers get overloaded, it's not an advisable time to sync.
Ancestry rolled out an improved mobile app about a week ago, this was announced on the (US) blog as well as the message boards. There have been users reporting they're experiencing dupes being created since that roll-out.
Don't shoot the messenger.