Multiple fetch requests NOT executed in async on Chrome on Windows

I am developing a simple website using Svelte, with a frontend server in Svelte and a backend server in NestJS. Currently, I'm working on my local machine.

The issue:

I am sending a request from my website to my "frontend server endpoint" in Svelte (located in the +server.ts file). This request is then forwarded to my NestJS server.

I'm using Promise.all to send 6 parallel requests from my website to the Svelte server. The Svelte server then reroutes these requests to the NestJS server and waits for the responses (since it's a heavy process, it typically takes 4-5 seconds).

All the requests are sent instantly from the website, I can verify this from the network tab. However, the Svelte server takes a significant amount of time (around 6-7 seconds) to actually receive these requests. It receives the first request and then it slows down. I don't understand why this delay is happening.

In my +server.ts file, I'm using async/await. My initial thought was that the Svelte server might be blocked while awaiting the NestJS server's response. However, I expected that the Svelte server would handle the async/await code for me, potentially creating workers or otherwise managing the asynchronous operations. Is my assumption incorrect?

Thanks!

Update

It is not Svelte related. I investigated (keeping in mind @Peppe L-G comment) and this is what I found out:

I created a simple HTML file with this code:

<script>
    fetch("https://httpbin.org/delay/5", { method: "GET" }).then(() => {
      console.log("1");
    });
    fetch("https://httpbin.org/delay/5", { method: "GET" }).then(() => {
      console.log("2");
    });
    fetch("https://httpbin.org/delay/5", { method: "GET" }).then(() => {
      console.log("3");
    });
    fetch("https://httpbin.org/delay/5", { method: "GET" }).then(() => {
      console.log("4");
    });
    fetch("https://httpbin.org/delay/5", { method: "GET" }).then(() => {
      console.log("5");
    });
  </script>

My expectation was to see the console.log to be executed almost at the same time. The API endpoint will reply after 5 seconds, simulating a heavy request. Everything is executed synchronously! A fetch is executed only after that the previous one is done. The same code, in nodeJS, is executed asynchronously. I am using the latest chrome version in Windows 11.