Contacts sync stuck updating on Moto E 2G My mom's Moto E (2nd Generation) has the following problem: after an OS OTA update (to v 5.1 security fix 2016-03-16), the contacts refuse to sync. The sync rolling icon is constantly showing, there are no contacts available, and the battery drains like crazy. She tried several restarts, and also left it alone for almost a day - no dice; the app is currently still "updating contacts". 

I logged into her Google account using a browser - all looks well, and all the contacts are there. My dad has the exact same phone and OS, and no issues with his contacts - so I'm clueless as to how to continue or who to contact.

Things I've tried (remotely with her :( ):


Turn contacts sync off and on under accounts
Remove the entire Google account and add it again  -everything syncs but contacts
Erase the cache of the contacts app


Any ideas how to proceed? Is this an OS, app, or Google account issue?
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 :(.