Lightroom always gets stuck while syncing to mobile

I am running Lightroom CC 2015.7 on Windows 7.  I have a catalogue with 1,356 photos spread out over 4 collections.  All four collections are synced with Lightroom mobile.  After syncing the first ~100 photos, it stopped and has been hanging on "syncing 1,207 photos" for hours.

This is not a new problem.  I have had this happen with every single catalog I've created over the last few weeks.  I will always have to force Lightroom to restart multiple times for syncing to fully complete. 

I spent 90 minutes on the phone with Adobe support today.  Steps we took to solve the problem:

- sign out and back into Lightroom

- sign out and back into creative cloud

- pause and restart syncing in the catalog

- pause and restart syncing on the collections

- pause and restart syncing in the creative cloud desktop app

- delete all synced cloud data and start over

- delete syncdata in \AppData\Local\Adobe\Lightroom\Caches

- delete everything in the Windows temp folder

- disable everything in startup and disable all non-Windows services

- check the hosts file for anything that could be interfering with communication with adobe servers

Nothing has fixed the problem.  I just tried switching computers and syncing photos from a brand new laptop running Windows 10, everything recently installed for the first time.  The laptop exhibits the same exact behavior.  Files begin to sync as they should, and then it just stops and hangs at a certain point. 

Syncing between desktop and mobile has been very inconsistent for quite some time.  I use an iPad pro to cull my images using pick flags and star ratings.  As an example, lets say I gave 5 stars to 150 images, and a "picked" flag to 500 images.  When I open Lightroom on my desktop and create smart collections for "5 star" images and "picked" images, it will show 100 with 5 stars and 300 flagged as picked (made up numbers, but it's always off by a lot).  I will need to sign out and back in and restart Lightroom multiple times for it to show all of my ratings/flags. Sometimes, I can't get it to completely sync all of my ratings/flags no matter how many times I restart, sign in/out, delete the cache, etc. 

One last note in case it's relevant -- I currently have Lightroom open and it is still stuck on "syncing 1,207 photos".  When I try any online gaming, there is a fair amount of lag.  As soon as I close Lightroom, the lag stops.  I have Verizon FIOS 100mbps up/down, normally never any problems with lag.  There isn't any data being uploaded to the adobe servers, because it's just hanging at 1,207 photos permanently, yet it seems to be causing lag while gaming that goes away immediately after closing Lightroom.  Very odd. 

Thank you in advance for any suggestions -- I'm at a loss of what to try next!