Can't connect to some wifi networks with iOS 9

After upgrading my iPhone 6 to iOS 9 I am not able to find the wifi network in the office. My colleagues have the same problem.

It worked fine with iOS 8.

With iOS 9 I can connect to other wifi networks e.g. at home.

I can connect to the office wifi network with my PC but it doesn't show up on my iPhone.

Is this a known issue that some wifi networks/protocols are not supported in iOS 9?