More information:
Problem with hte address does not appear to be a mattermost server - https reroute in nginx config. So obviously issue with https SSL by Letsencrypt. (I converted the CA and CRT to PEM to make it work with desktop browsers. without having to be insecure.)
Since nginx has disabled the reroute, it allows Android APP to connect but as I have gitlab SSO it wont login using gitlab linkbox. No logs are generated that I can find.
So detects server but just doesnt want to use SSO login, Is there a way to push SSO to android app? Seems like having the ability to login to the android app via gitlab login would fix this.