Still no luck =(
I removed the client id from the gateway configuration, and added a sub to mcThings/Testing in the Android app.
I also tried rebooting the CloudMQTT server, this is the startup details that appear under the server log
1507051319: mosquitto version 1.4.10 terminating
1507051319: mosquitto version 1.4.10 (build date Thu, 25 Aug 2016 15:32:03 +0100) starting
1507051319: Config loaded from /var/lib/mosquitto/10933/mosquitto.conf.
1507051319: Opening ipv4 listen socket on port 20933.
1507051319: Opening websockets listen socket on port 30933.
1507051319: Opening ipv4 listen socket on port 10933.
1507051406: New connection from my.phones.ip.address on port 10933.
I can see my phone connecting in the server logs, but I don't my computer (mcGateway) connect.