I solved this problem by deleting all test users and expiring all pending test flight iOS compilations. I think this is actually what Apple is asking us to do, but it's not as clear when looking at it at first time. The last thing I did was expiring the iOS compilations. Unfortunately I don't have any screenshots available because the compilations disappeared from the screen after the app transfer was successful, but just make sure you expire all pending test flight iOS compilations and hopefully Testflight will be listed as checked on the checklist for your app transfer. Good luck. Best Regards, Ulysses Alves