Fetch only works if there is a '?#' in the current url of the current page using react?

I develop a react project and my problem is that fetch only works if I have an additional '?#' at the end of the current url of the page I am currently located.

cors origin is set to '*' on the target server.

My fetch request:

fetch("http://localhost:3000/getAIRes/" + input)
  .then((res) => res.json())
  .then(
    (result) => {
      console.log(result);
    },
    (error) => {
      console.log(error.message);
    }
  );

The behaviour of fetch if run at following locations:

• http://example.com/home => fetch throws an "TypeError: Failed to fetch" error.
• http://example.com/home?# => fetch works perfectly fine.

I tried using axios, an alternative to fetch, but neither do i get a response nor is a error thrown:

axios.get("http://localhost:3000/getAIRes/" + input).then(
  (response) => {
    console.log(response.data);
  },
  (error) => {
    console.log(error);
  }
);

How is this possible?