Creating a test "Hello world" project works. I went back to an older branch and found that it still works. So I went back to my latest branch and discovered that it works once again. I guess if anybody else is experiencing this issue, I would recommend going back to a known working branch, build + upload the app, then go back to the latest.

Did you ever get this resolved? I am facing the same issue (I think). Testflight works, but it's a pain not being able to debug in realtime.