I've seen similar problems when kamailio runs on a server with NAT. Even if kamailio sends from port 5060, a NAT rule that usually maps that to 5060 when sending can sometimes end up translating the port to something else (even while kamailio is technically still using 5060 before the NAT changes it).
There was something similar mentioned in this mailing list in the last year or two.

James

On Sun, 23 Feb 2025 at 07:15, Brett Nemeroff via sr-users <sr-users@lists.kamailio.org> wrote:
I can't answer exactly why it happened. System behavior when the root file system is exhausted is very unpredictable and this behavior, while strange, doesn't really surprise me. I wouldn't expect anything to be done to allow proper functionality with an exhausted filesystem. I also don't think that this really points to a larger problem. It's also likely that there were a lot of other odd behaviors that you didn't realize!

I'd consider what is exhausting your filesystem. Probably logs. And move that to a mount point that isn't part of the operating system. 

Good luck!
-Brett

On Thu, Feb 20, 2025 at 2:20 AM Leonid Fainshtein via sr-users <sr-users@lists.kamailio.org> wrote:
Hi,
I am using Kamailio v.5.8.4 on Ubuntu 24.04, kernel 6.8.0-51-generic
In the configuration script I explicitly set $fs="udp:adrr:port". In normal situations, it works properly and I see that the UDP SIP requests are sent from the requested IP and port.
Due to some reasons, free space on the server root filesystem was exhausted.  
I cleaned up the file system and everything looked good except the fact that Kamailio started to send messages from ephemeral IP ports instead of the port defined in $fs. 
Restart of Kamailio didn't solve the problem.
But the server reboot fixed the issue.
I don't understand how the lack of free disk space can cause such a problem and I'm afraid that there is another reason that I am missing. 
Has anybody seen such a problem?

Best regards,
Leonid 
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========================================================
Brett Nemeroff
Voice Fox Telephony LLC
Office: 512-670-8369
Email: brett@voicefoxtelephony.com
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