Captive portal is showing full max time.

[somendra]

Hi!
we are using pfsense as firewall in our wireless network.but now we are getting many times that captive portal status is full(100 or 100+),and this creates trouble to new connected user something like splash page pop-up over and over,abnormal IP allocation by Dhcp server.Every time rebooting pfsense box fixed the issue but i want to fix it by another way  rather than rebooting evrytime.

Any idea to fix it?
Thanks in advance for your kind help.!