I have not looked at the code, but is the sync protocol using port 80/8080, or something else?
Most products just gave up on custom TCP/IP ports as the firewalls people set up for home and office use just cause grief. Many end user postings here recently related Windows 10 upgrades would point at a trend. So many apps just use port 80/8080, maybe an https:// connection would be all this needed for a secure connection?