I'm using Firefox (108.0, MacOS 13.1).
When I run this project, the browser debugger shows there's some 500 responses from the server.
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I added this code to the index.js, and the server console logs:

io.engine.on("connection_error", (err) => {
 // console.log(err.req); // the request object
 console.log(err.code); // the error code, for example 1
 console.log(err.message); // the error message, for example "Session ID unknown"
 console.log(err.context); // some additional error context
});

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I guess the problem is: the websocket connection was established successfully, but the polling connection failed.
So I tried to add a parameter to allow only polling:

const io = require('socket.io')(http, {
 transports: ['polling']
});

Then, the connection never establishes successfully. The browser sends requests and gets 500 responses infinitely. The server also gets "Session ID unknown" infinitely.
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Looks like a new connection starts to establish when the previous connection hasn't finished establishing.

I've tried the latest version (4.5.4) of "socket.io" and "socket.io-client", the behavior is the same.
And I found the polling connection can be successfully established in the latest version of Chrome, but failed in Edge as in Firefox.

How can I solve this?