os-shadowsocks udp-over-tcp mode not working

[gregor-hh]

• [X ] I have read the contributing guide lines at https://github.com/opnsense/plugins/blob/master/CONTRIBUTING.md
• [X ] I have searched the existing issues, open and closed, and I'm convinced that mine is new.
• [X ] The title contains the plugin to which this issue belongs

Describe the bug
If I connect to my Shadowsocksserver (Mode: TCP and UDP)(on OpnSense) via iOS App (shadowrocket) and enable UDP over TCP (sp.udp-over-tcp.arpa or sp.v2.udp-over-tcp.arpa)
It doen't works.. Instead of, the OPNsense show thist for each UDP request:
2026-01-27T23:09:16.335536049+01:00 ERROR tcp tunnel :15252 -> sp.v2.udp-over-tcp.arpa:0 connect failed, error: Can't assign requested address (os error 49)
Also tried to enable Fragmentation checkbox -> no success.

The version of os-shadowsocks is 1.3

TCP is working perfect.

To Reproduce
Steps to reproduce the behavior:

1. Connect to Shadowsocks with enabled UDP-Relay (iOS App - Shadowrocket) -> sp.udp-over-tcp.arpa or sp.v2.udp-over-tcp.arpa checked
2. Go to speedtest (NET) website and start a test or start a Network Utility App in my case "Net Analyzer" and do a a DNS resolution test. (DNS must be overided for example 1 . 1 . 1 . 1 53
3. Check Logs in OPNsense UI -> System -> Log FIles -> General
4. See error --> ERROR tcp tunnel :15252 -> sp.v2.udp-over-tcp.arpa:0 connect failed, error: Can't assign requested address (os error 49)

Expected behavior
I expect a functional udp dest ports UDP-over-TCP

Screenshots

Relevant log files
Not muched log, maybe there is an option to anbale a debug log fpr shadowsocks?

Additional context
Add any other context about the problem here.

Environment
OPNsense on proxmox, CPU Type Host

OPNsense 25.7.11_2-amd64.
Intel(R) Core(TM) i3-8100T CPU @ 3.10GHz (4 cores, 4 threads)
VirtIO (paravirtualized)