Hi,
Do you have persistent realm? If there is persistent realm, it might contribute to the issue. You can set "Validation Period Enabled"
Validation Period Enabled (persistent sessions only)
If set, the specified value determines the maximum period between agent calls to the Policy Server to validate a session. Session validation calls perform two functions: informing the Policy Server that a user is still active and checking that the user's session is still valid.
Regards,
Kar Meng