Contacts sync stuck updating on Moto E 2G
Well, I had to reset the phone to its factory state, and reinstall all from scratch. I've seen this question asked on several forums, with no satisfactory answer. 

If you come across one in the future, ping me, and I'll reopen the question. Until then, just restore your phone. Tons of work for (what I'm sure is) a very simple sync bug :(.