I see that you are using https to a private IP, which indicates that you don't have a valid trusted certificate.
Please make sure that you have a trusted certificate on both your APs/controller and on ClearPass.
Without these certificates, you will run into all kinds of unexpected issues like not redirected, no pop-ups, unable to authenticate, because the client blocks insecure access.
Do you have trusted certificates on both controller/AP (the name for that certificate needs to be entered in the NAS IP address in ClearPass Guest) and your ClearPass?