NOTE: if you have localizations, you'll need to delete Test Information for each localization. If you just delete English, the localization dropdown will disappear and there will still be hidden text in some of the fields for the non-English localizations.
I had performed all the steps as well, but still was getting the "remove all builds and testers from the app you want transferred and clear each information field below Test Information" requirement. What I realized is I needed to add info back into the Test Information and save. This made the localization dropdown re-appear, and I had to go through each language and delete each field, clicking save after each language, and making sure English was the last language to clear the fields.
Hope this helps someone - I have been pulling my hair out all day.
Topic:
App Store Distribution & Marketing
SubTopic:
TestFlight
Tags: