The screen is stuck on: "We are launching your Citrix application, please hold on..."
It could happen that your Citrix application is not started and you will see that it's stuck on the message above. In that case, start the developer console of your browser. Usally this is done by the F12 key. Check what kind of error message is displayed in the "Console".
This error message tells you that the HTML5SDK is not installed. Please try to download and install the Receiver for HTML5 SDK. Choose the "Receiver SDK 2.x.x for HTML5".