mux causes bufferbloat and breaks iperf3 download test

[arinc9]

Which version of V2Ray are you using?

v5.29.2

What abnormal phenomenon do you see?

When mux is enabled, it causes great delay when there's load. Speedtest result shows unusually high RTT when under load.

https://www.speedtest.net/result/c/74b36398-b42d-4d6c-8f71-8d4cdb345cc2

It also breaks downloading using iperf3. Client side is stuck at:

$ iperf3 -c server -R
Connecting to host server, port 5201
Reverse mode, remote host server is sending

Server side continues until the client stops:

-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------
Accepted connection from server, port 53494
[  5] local server port 5201 connected to server port 53500
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec  11.2 MBytes  94.3 Mbits/sec    1   1.12 MBytes       
[  5]   1.00-2.00   sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]   2.00-3.00   sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]   3.00-4.00   sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]   4.00-5.00   sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]   5.00-6.00   sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]   6.00-7.00   sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]   7.00-8.00   sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]   8.00-9.00   sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]   9.00-10.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]  10.00-11.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]  11.00-12.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]  12.00-13.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]  13.00-14.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]  14.00-15.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]  15.00-16.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]  16.00-17.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]  17.00-18.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]  18.00-19.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]  19.00-20.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
[  5]  19.00-20.00  sec  0.00 Bytes  0.00 bits/sec    0   1.12 MBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-20.00  sec  11.2 MBytes  4.72 Mbits/sec    1             sender
iperf3: the client has terminated

What normal performance do you expect to see?

This is the result without mux.

https://www.speedtest.net/result/c/efab3adf-b0a2-41af-875c-4c7a7e629a9d

iperf3 works normally without mux.

Please attach your configuration

Server configuration:

{
  "log": {
    "level": "info"
  },
  "inbounds": [
    {
      "port": port,
      "protocol": "vmess",
      "settings": {
        "clients": [
          {
            "id": "UUID"
          }
        ]
      },
      "streamSettings": {
        "sockopt": {
          "mptcp": true
        }
      }
    }
  ],
  "outbounds": [
    {
      "protocol": "freedom"
    }
  ]
}

Client configuration:

{
  "inbounds": [
    {
      "port": 12345,
      "listen": "127.0.0.1",
      "protocol": "dokodemo-door",
      "settings": {
        "network": "tcp,udp",
        "followRedirect": true
      },
      "streamSettings": {
        "sockopt": {
          "tproxy": "tproxy"
        }
      }
    }
  ],
  "outbounds": [
    {
      "protocol": "vmess",
      "settings": {
        "vnext": [
          {
            "address": "server",
            "port": port,
            "users": [
              {
                "id": "UUID",
                "security": "zero"
              }
            ]
          }
        ]
      },
      "streamSettings": {
        "sockopt": {
          "mptcp": true
        }
      },
      "mux": {
        "enabled": true,
        "concurrency": 8
      }
    }
  ]
}