TestFlight: Beta testers can't access latest version

Question

Our latest version passed review yesterday, and the beta testers (~10 people) received their notification that the build is ready to test on iOS. When they click the TestFlight link in the e-mail, it opens a screen that says: "Couldn't Load App. This build is no longer available." With a "Try Again" button. I have tried removing and re-adding all testers, and that didn't do much if anything. Also, a NEW tester that was only added to the new version could download it with no problem. This only appears to affect users that have an older version already installed?

Please help!

Answer 1

Instead of adding individual testers to the build, we started using the "External Groups" functionality in TestFlight. This seems to have resolved the issue for us, however there is still clearly an issue with individual testers getting access to successive builds.