I'm trying to reach TestFlight on iTunesConnect but it keeps only the loading spinner and do not show anything. I've tried with Chrome and Safari without success.
In my other application on the very same account everything works correctly.
I've already written to support waiting for their response.
My issue was resolved from the support team. They didn't provide me full details what caused this, however after sending them needed information(including page source code) they fixed it on next day.
So if you experience the same, I advise you to contact them(via iTunesConnect).