>This sounds like a captive portal "freezing" issue I have seen before. 
>When this is happening, can un unrecognized client log in normally?

Sometimes I can, sometimes the mac address is not even registered in captive
portal at all and the captive portal does not show even if I cleaned the
memory and removed all the users from the captive portal diagnosis page
(unrecognized all computers from captive portal).

What should I do if I face this again?

Thanks
Rendra