HomeKit broken: video live stream no response away from home

This is a question for someone with expertise in HomeKit. My HomeKit setup consists of an Aqara G2H Pro hub camera and a HomePod mini.

Live stream video works fine on the home network, but not at all away from home via cellular data. I can view motion-triggered recordings via data; I can cycle the recording light on the camera via data; I can view live stream on the Aqara native app via mobile data.

Trying to view the livestream on HomeKit just leads to a spinning wheel on the image followed by no response.

This was working briefly when I first set up the HomeKit, and stopped working after a day or two - possibly after the update?

Everything has been factory reset, deleted and re-set up, logged out of iCloud, etc etc many times. Routers have been reconfigured and reset to factory, apps reinstalled.

Nothing seems to work and Apple Technical support have no idea, nor Aqara and simply refer me to each other.

Any suggestions? Or do I give up on Apple’s venture into smart home technology?