Firstable, you are running an old version of ISE. I would recommend the stable 1.4 minimum.
Test the URL configured on the WLC L3 from your PC and check if the login page is displayed. The URL that I am referring is the one located at
WLC GUEST SSID -- > SECURITY TAB --- > LAYER 3 --- > URL at the bottom.
If it does not give you something similar to the attached screenshot, then you have a DNS misconfiguration.
Attached picture is from 1.4 version GUEST PORTAL.
Another option could be if you have more than 1 entry in the WLC ---> SSID --- > AAA Servers. Round Robin DNS does NOT work properly on Webauth. If you are using Load balancers like F5, then you have probably something misconfigured as well.
Check both and let me know.
thanks