Hysteria2 inbound causes Discord WebRTC/screen share lag in TUN mode, while sing-box Hysteria2 works normally

[ARAMU2728]

Integrity requirements

• I have read all the comments in the issue template and ensured that this issue meet the requirements.
• I confirm that I have read the documentation, understand the meaning of all the configuration items I wrote, and did not pile up seemingly useful options or default values.
• I provided the complete config and logs, rather than just providing the truncated parts based on my own judgment.
• I searched issues and did not find any similar issues.
• The problem can be successfully reproduced in the latest Release

Description

Summary

Discord voice works normally through Xray Hysteria2 inbound, but Discord screen share / video stream has heavy lag and stuttering when the client uses TUN mode.

The same VPS and the same client-side network were tested with sing-box / Hiddify Hysteria2, and Discord screen share worked normally there.

The issue appears only with Xray-core Hysteria2 inbound.

Environment

Server:

• OS: Ubuntu
• Panel: 3x-ui
• Core: Xray-core
• Xray version: 26.4.25
• Protocol: Hysteria2 inbound
• Transport/security: Hysteria2 + TLS + ALPN h3

Client:

• OS: Windows 11
• Client: Throne, INCY, Happ, Hiddify
• Mode where issue happens: TUN mode
• Application affected: Discord

Observed behavior:

• Discord voice works normally
• Discord screen share / video stream has heavy lag and stuttering

Important comparison

The same VPS was tested with Hiddify / sing-box Hysteria2.

Result:

• sing-box / Hiddify Hysteria2: Discord screen share works normally
• Xray-core Hysteria2 inbound: Discord screen share lags heavily

So this does not look like a VPS, CPU, RAM, swap, or provider network issue.

Additional clarification

I also tested Hysteria2 in Hiddify Panel when it was using Xray-core for Hysteria2.
In that case, Discord screen share / video stream also had the same lag.

When Hysteria2 was handled by sing-box / Hiddify-core on the same VPS, Discord screen share worked normally.

So the issue seems related specifically to Xray-core Hysteria2 handling, not to 3x-ui itself and not to the VPS.

The lag is visible on the viewer side: other Discord users who watch my screen share see heavy stuttering / lag.
Discord voice stays normal at the same time.

I like Xray-core and would prefer to continue using it.
I am reporting this because I would like Hysteria2 in Xray-core to work reliably for Discord screen sharing / video streaming, the same way it works with sing-box Hysteria2 in my tests.

Reproduction Method

1. Create a Hysteria2 inbound in Xray-core / 3x-ui with TLS and ALPN h3.

2. Connect from a Windows 11 client using Throne, INCY, Happ, Hiddify

3. Enable TUN mode in the client.

4. Route Discord traffic through the Hysteria2 outbound.

5. Join a Discord voice channel.

6. Start Discord screen share or video stream.

7. Observe the result:

   • voice works normally
   • screen share / video stream has heavy lag and stuttering

8. Repeat the same test on the same VPS with sing-box / Hiddify Hysteria2.

9. Observe the comparison:

   • sing-box / Hiddify Hysteria2 works normally
   • Xray-core Hysteria2 inbound lags with Discord screen share

Client config

Details

Primary client: Throne on Windows 11
Core process: ThroneCore
Core command line:
C:\Users\PC-User\AppData\Roaming\Throne\ThroneCore -port 7514
Mode where the issue is clearly reproduced: TUN mode

Outbound used for affected Discord traffic: hysteria2
The full internal Throne client config is generated by the GUI and stored internally.

I could not export the full generated config from the Throne UI.
However, the Throne client log confirms that Discord UDP/WebRTC traffic is routed through hysteria2 in TUN mode:
Discord.exe -> outbound/hysteria2[proxy] -> 104.29.147.43:19307

Discord.exe -> outbound/hysteria2[proxy] -> 104.29.147.151:19337

Discord.exe -> outbound/hysteria2[proxy] -> 162.159.137.232:443
Additional clients were also tested:

INCY
Happ
Hiddify

The same Discord screen share / video lag was observed with Xray-core Hysteria2 inbound.
Important comparison:

When using sing-box / Hiddify Hysteria2 on the same VPS, Discord screen share works normally.
In System Proxy mode the screen share does not lag, but this is likely because Discord real-time UDP/WebRTC traffic can bypass the system proxy.

Server config

Details

{
  "log": {
    "access": "none",
    "dnsLog": false,
    "error": "",
    "loglevel": "warning",
    "maskAddress": ""
  },
  "routing": {
    "domainStrategy": "AsIs",
    "rules": [
      {
        "type": "field",
        "inboundTag": [
          "api"
        ],
        "outboundTag": "api"
      },
      {
        "type": "field",
        "outboundTag": "blocked",
        "ip": [
          "geoip:private"
        ]
      },
      {
        "type": "field",
        "outboundTag": "blocked",
        "protocol": [
          "bittorrent"
        ]
      }
    ]
  },
  "dns": null,
  "inbounds": [
    {
      "listen": "127.0.0.1",
      "port": 62789,
      "protocol": "tunnel",
      "settings": {
        "address": "127.0.0.1"
      },
      "streamSettings": null,
      "tag": "api",
      "sniffing": null
    },
    {
      "listen": "0.0.0.0",
      "port": 44572,
      "protocol": "hysteria",
      "settings": {
        "clients": [
          {
            "auth": "redacted",
            "email": "redacted"
          }
        ],
        "version": 2
      },
      "streamSettings": {
        "hysteriaSettings": {
          "auth": "",
          "udpIdleTimeout": 60,
          "version": 2
        },
        "network": "hysteria",
        "security": "tls",
        "tlsSettings": {
          "alpn": [
            "h3"
          ],
          "certificates": [
            {
              "buildChain": false,
              "certificateFile": "/root/cert/ip/fullchain.pem",
              "keyFile": "/root/cert/ip/privkey.pem",
              "oneTimeLoading": false,
              "usage": "encipherment"
            }
          ],
          "cipherSuites": "",
          "disableSystemRoot": false,
          "echForceQuery": "none",
          "echServerKeys": "",
          "enableSessionResumption": false,
          "maxVersion": "1.3",
          "minVersion": "1.2",
          "rejectUnknownSni": false,
          "serverName": ""
        }
      },
      "tag": "inbound-44572",
      "sniffing": {
        "enabled": false,
        "destOverride": [
          "http",
          "tls",
          "quic",
          "fakedns"
        ],
        "metadataOnly": false,
        "routeOnly": false
      }
    }
  ],
  "outbounds": [
    {
      "tag": "direct",
      "protocol": "freedom",
      "settings": {
        "domainStrategy": "AsIs",
        "redirect": "",
        "noises": []
      }
    },
    {
      "tag": "blocked",
      "protocol": "blackhole",
      "settings": {}
    }
  ],
  "transport": null,
  "policy": {
    "levels": {
      "0": {
        "statsUserDownlink": true,
        "statsUserUplink": true
      }
    },
    "system": {
      "statsInboundDownlink": true,
      "statsInboundUplink": true,
      "statsOutboundDownlink": false,
      "statsOutboundUplink": false
    }
  },
  "api": {
    "tag": "api",
    "services": [
      "HandlerService",
      "LoggerService",
      "StatsService"
    ]
  },
  "stats": {},
  "reverse": null,
  "fakedns": null,
  "observatory": null,
  "burstObservatory": null,
  "metrics": {
    "tag": "metrics_out",
    "listen": "127.0.0.1:11111"
  }
}

Client log

Details

INFO[0003] outbound/hysteria2[proxy]: outbound packet connection to 104.29.147.43:19307
INFO[0008] router: found process path: C:\Users\PC-User\AppData\Local\Discord\app-1.0.9234\Discord.exe
INFO[0008] outbound/hysteria2[proxy]: outbound connection to 162.159.137.232:443
INFO[0011] router: found process path: C:\Users\PC-User\AppData\Local\Discord\app-1.0.9234\Discord.exe
INFO[0011] outbound/hysteria2[proxy]: outbound packet connection to 104.29.147.43:19307
INFO[0058] router: found process path: C:\Users\PC-User\AppData\Local\Discord\app-1.0.9234\Discord.exe
INFO[0058] outbound/hysteria2[proxy]: outbound packet connection to 104.29.147.151:19337

Server log

Details

This is the available x-ui journal output containing Xray-core messages. I could not obtain a separate Xray-core debug log from 3x-ui.
Xray starts successfully:
Apr 29 18:16:36 ubuntu /usr/local/x-ui/x-ui[42838]: INFO - XRAY: infra/conf/serial: Reading config: &{Name:bin/config.json Format:json}

Apr 29 18:16:36 ubuntu /usr/local/x-ui/x-ui[42838]: WARNING - XRAY: core: Xray 26.4.25 started
No runtime Xray errors were shown during the Discord screen share lag.
Older unrelated startup errors were caused by temporary test configurations:

BrutalUp must be at least 65536 bytes per second
failed to parse certificate / both file and bytes are empty

These errors were fixed before the actual Discord screen share test.
During the lag:

Xray was running
UDP kernel error counters did not increase
UDP socket queue did not grow
no interface drops
no fq_codel drops
CPU/RAM were not exhausted