When using OCR Synching on a network with a firewall, you must enable the Bonjour service that apple uses.
According to this document:
https://support.apple.com/en-us/HT202944
The following ports are used by Bonjour:
UDP 1900
UDP 5350
UDP 5351
UDP 5353
You should be able to verify that you are seeing traffic on both sides of network. There are some apps that will help see the traffic.
Android:
https://play.google.com/store/apps/details?id=com.grokkt.android.bonjour&hl=en
Apple iOS:
https://itunes.apple.com/us/app/discovery-bonjour-browser/id305441017?mt=8
You should see services being advertised with names that start with “_OnCue”, such as
_OnCue._tcp.
_OnCueMaster._tcp
_OnCueTrans._tcp
The other On Cue specific ports that need to be open:
3700 TCP - sending transmitter page requests
3701 UDP - listening for transmitter heartbeat
8888 TCP - Sync push/pull