Could you try to trigger a "Delete all Data" via Lightroom Desktop preferences -> Lightroom Mobile. With that you would start from zero.
When you still come to the point that sync hangs please send me a LR Desktop diagnostig log - best as a private message with a downloadable dropbox link.
You can trigger the log via LR Desktop prefereneces -> Lightroom Mobile and when you hold down the alt key you will notice a generate diagnostic log button
Thanks. Delete all Data worked, however I was originally hoping to avoid since it would mean losing work that I had done on Lightroom Mobile. When I started over yesterday I had Lightroom mobile pull in pictures from my camera roll and then noticed the sync again wouldn't work. I noticed the most recent pictures I had taken using an app called Cortex Cam. This app basically takes several pictures and "merges" to create a sharper handheld with more detail, effectively creating a 12 megapixel image (cool app, was even featured by Dan Rubin in the Guardian recently). I deleted these photos from my iPhone, then once again did a "Delete all Data" and started from scratch again. So far, after a day of use, no issues syncing. Everything is working.
Not sure if the Cortex Cam app was the problem, but going forward if I use that app, I'll just make a point of not having Lightroom Mobile open to import it.
Glad that it's working again. I'll double check if the Cortex Cam app-images interfere Lr Mobile in a bad way. - Guidio