TestFlight iOS App get-task-allow Issue
I had this and solved it.
Xcode was using a different provisioning profile from the one I had expected it to - it was signing the build with a distribution certificate, but had created a development provisioning profile.
It turned out that the distribution certificate was somehow invalid. I discovered this by setting the provisioning profile explicitly in the project, which then prompted xcode to give me an error to tell me there were problems.
A good place to start solving these issues is to look in the build log, at the codesign step - there will be a line line:
Using code signing identity "iPhone Distribution: XXXXXX" and provisioning profile "YYYYYY" (<..guid...>)
Check this line says the certificate and profile you expect, and that the signing identity and profile are both distribution ones.