Hi @Chris_G
There’s no reason I can think of for this being the case. So if I’m understanding correctly your controller is on the public Internet outside of your LAN.
Have you tried rebooting your UniFi devices? I’ve seen it before where UniFi devices are stuck in a rejection state.
If you SSH to one of your UniFi devices and run the info command it will tell you why it can’t talk to the controller.