Just uploaded a v1.0 build 3 bundle.
It's showing in itunesconnect as the currently selected external tester bundle.
It sent out the emails OK (v1.0 build 3).
Click on the email and try to install, it opens TestFlight App, which only lists v1.0 build 2.
With the 'app already installed' error.
Or if you go direct to the TestFlight App, it only shows v1.0 build 2.