Peers session expires

Good morning. Im asking for help because i had some failures in my asterisk network. The problem is that, in some peers, the session expires and i understand that it happens because the peer cant register again.

When that happens If I write “sip show peer xxxxxxx” you can see that “Expire” has the value “-1” and the Status is “UNREACHABLE” or “UNKNOWN”, then I must prune that peer or reboot the VoIP router. The VoIP routers i am having trouble have this menu, Im testing it with different values but i cant solve the problem.

Registration Expire Timeout[units:s]: 300
Registration Retry Interval[units:s]:60
Session Expire Time[units:minuts]:30
Min Session Expire Time[units:minuts]: 2

I hope you can help me. Thank you.