Hey man thanks heaps for the help.
Ok im testing exactly as you describe. I upload a beta version for External Testing. It takes around 24hrs to be reviewed. Then I can test it in TestFlight (I have my External Testers emails added to the list).
I *think* the problem might be what you said in the second part of your response, that the GameCenter stuff needs to be live. I dont have a Leaderboard I only have achievments.
If I go to 'App Store' and click on the Version, then scroll down to where it has GameCenter info. It looks like this:
Looks like GameCenter is active? The toggle is green...
But if I go to Features > GameCenter, I can see that the Achievements say 'Not Live'...
So... Im thinking, the version I am trying to beta test is 1.0.3, and I need to make the achievements 'Live' for that version... but I dont know how to do that.
I believe you wont have to worry about them going live while testing as long as you have them enabled under information page. They go live on official release so you should be set to go on the next test.