Brand new MacBook Pro (13-inch, 2016, Four Thunderbolt 3 Ports)
Lightroom version: CC 2015 
License: Creative Cloud
Operating system: Mac OS 10
Version: 10.12 
Lightroom catalogue is on external hard drive, was syncing with iPad just fine until I changed to a new computer.
Now I have 5134 photos in my MacBook catalogue
8 photos on Lightroom.com
204 photos on iPad lightroom
MacBook goes through the motions of syncing and uploading, but they don't appear on the web-page or the iPad.
How do I get them to sync? I already tried deleting the sync file on the Mac, no different,
Whatever we sync from the Lightroom desktop to Lightroom mobile, its the same thing on the Lightroom web app.
You need to check, how many devices you are syncing with Lightroom desktop. Lightroom Mobile and Lightroom web should show the same images, same edits and everything identical.