I submitted a new version of my app via Xcode 7.1 successfully. Then noticed the build was stuck in "Processing" longer than usual.
I followed Scotch's suggestion by increasing the build number, while keeping the same version, and submitted again from Xcode. This time the new build became available for testing within 5 minutes.
I was then able to select that build and clicked on Start testing. My internal testers received the notification emails and were able to test the new version via the Testflight app.
