This occurs when the radius service on CPPM handling the captive portal request is not configured with proper enforcement profiles.
We must make sure that "Guest Do Expire" is added to the Enforcement profile.
Please find the steps below to map this profile with the service.
Login to CPPM and navigate to the Radius service which handles the Guest authentication.
Edit the service goto the Enforcement tab and modify the enforcement policy.
Navigate to Rules tab and add the profile as shown below.
Add the profile and save the changes.
Details about "Guest Do Expire" profile.
It is a Post authentication profile with the below details.