Following the release of sing-box 1.4.0, when sing-box used as shadowsocks server tcp data transfer tends to freeze when there is a spike in transmitted traffic in long sessions.
Some of the scenarios where this issue is observed include:
- While tailing long log files through SSH: The SSH session becomes stuck after a few seconds.
- During RDP sessions: Similar freezing behavior is noticed when a window is opened or moved. This is likely due to the increase in traffic usage caused by screen redraws.
- Turn connections via TCP also gets stuck after a few seconds of sound or video transmission.
This bug has been reproduced across all versions from 1.4.0 through to 1.5.0-rc.4. However, it is not reproducible in versions earlier than 1.4.0. Enabling multiplexing on client(h2mux or smux) seems to fix the problem, and the issue does not present itself under such conditions.
This issue doesn’t seem to be related to the client version. It has been reproduced in both sing-box and xray ss clients. Also, nothing suspicious can be found in the logs.