By the way, i didn’t find how to configure/disable SIP user agents you talk about. Where can i do that?
So i guess to solve this issue, you have to set UDP NAT session timeout to very short time… ?
SIP user agents are the SIP devices you are using through your NAT. It could be your IP-PBX if on premises or your IP phones if your PBX is in cloud.
Reducing UDP NAT sessions timeout to a value lower than SIP register refresh is not a good idea as by doing so incoming requests will often find a closed door. Neither is turning your PBX or phones off until their NAT sessions time out.
I usually flush all NAT sessions: security->firewall->connection tracking->flush.
Quick and dirty (very dirty)