Hundreds of unused states

[f005]

Hello, I am a new user of pfsense. Everything works fine. I got only one serious problem: some captive-portal users have hundreds of unused states. The users sometimes didn't login to the captive-portal before, some other clients are logged in to captive-portal.
The avarage of number of concurrent users is round about 50 users.
The maximum states I've defined to 5,000 states. (If I raise the maximum states my router sometimes stop working and I have to reboot it.)
The only port of several internet hosts (facebook, amazon,…) which tries to connect to my guest-clients is the tcp 443. How do i reset the unused states automatically or limit the number of states? Changing the limit per Host in firewall-rules doesn't work.

Many Thanks

(In screenshot the anonymized clients is only one client)