No audio in Android app

Deployed OpenVidu 2.17 to AWS and can access it via https://mycompany.com where I can see and hear others fine via the browser. Lets Encrypt cert installed and Chrome on my Mac asks for permission to access the camera and mic.
Integrated OpenVidu into our app where I can see others on the 2.17 instance and they can hear me (quietly), but I cannot hear them. Back to testing out the example OpenVidu app…
Reinstalled the (clean) demo Android app and connected it to my server. Important note - NOT using “:4443” at the end of the URL (just the https://mycompany.com URL) and I can see the others users. But again I cannot hear them and my outgoing audio is quiet.
This is on a Samsung Galaxy Tab A 2019 running Android 10. Speaker is set to max and is working fine as I play a phone ringing WAV file to get the tablet users attention.

The only changes I have made to the default code are ones to stop it crashing at startup - putting NULL checks in leaveSession.

Anyone got any ideas why I have no audio? The fact that the OpenVidu demo app and my app behave the same kind of implies its an Android issue, but I have used Zoom on this tablet fine before.

Thanks

Mat

Anyone got any ideas?