The image reveals a critical piece of information that changes the entire troubleshooting path: You are routing your traffic through Cloudflare ( Server: cloudflare , CF-RAY: ...-SIN ) before it ever hits your local Windows 11 IIS proxy ( X-Powered-By: ARR/3.0 ). [ 1 ] Your browser is sending the WebSocket request with compression enabled ( Sec-WebSocket-Extensions: permessage-deflate ), but IIS ARR 3.0 breaks when proxying compressed WebSockets over a third-party CDN like Cloudflare , leading to the instant connection crash and loop you are seeing. [ 1 ] To completely solve this, you need to strip that specific WebSocket compression extension header so IIS and Cloudflare can talk cleanly. The Fix: Force IIS to Strip WebSocket Compression Extensions You need to use the URL Rewrite module on your Windows 11 IIS site to forcibly clear the HTTP_SEC_WEBSOCKET_EXTENSIONS variable. [ 1 ] Step 1: Allow Server Variable Overrides in IIS Open IIS Manager . Click your main Windows 11 Se...