We noticed that there are some problems with playing of the private channels with the iOS 11 Beta version and we are currently checking into the matter. At the moment, we are unable to confirm if the issue is caused by the Zattoo app or the iOS Beta version.
Please not that it is possible that the problem might only be solved with the proper iOS 11 release in autumn 2017.
We suggest that you downgrade your iOS and reinstall iOS 10 until then. Here you can find instructions on how to do that.
Thank you for your understanding!