Why is cors-anywhere returning error message only for one specific address

Question

I have cors-anywhere server running together with my ReactJS project which I'm using to scrape some info from various pages. For one specific URL the system returns an error

https://www.fibank.bg/en/currency-rates

<b>Error when loading the page.</b><br /><br />
        The reason for this error could be add-on or extension in your browser.<br /><br />
        Please, check the active add-ons and extensions in your browser or try to open the webpage from another browser.<br /><br />
        If this error appears again, you can send us its ID (<b id="ide"> ... </b>) by email to  <a href="mailto:[email protected]">[email protected]</a>. We will provide you further instructions.<br /><br />
        Regards,<br />
        Fibank team<br /><br />

You can reproduce the same error I'm getting on the cors-anywhere demo page https://robwu.nl/cors-anywhere.html Below is the code I'm using in my project.

useEffect(() => {
    fetch(
      `http://localhost:8080/https://thehiddenurl`,
      )},
      {
        headers: {
          "Content-Type": "application/json",
        },
      }
    )
      .then((response) => response.text())
      .then((result) => {
        if (result) {
          const el = document.createElement("html");
          el.innerHTML = result;
          const arr = Array.from(el.getElementsByTagName("tr"));
          const filtered = arr.filter((el) => {
            return CURRENCIES.includes(getCurrencyStr(el));
          });
          filtered.forEach((el) => {
            const currentCurrency = getCurrencyStr(el);
            if (currentCurrency && currentCurrency in DEFAULT_CURRENCY) {
              DEFAULT_CURRENCY[currentCurrency].buy = el.children[4].innerHTML;
              DEFAULT_CURRENCY[currentCurrency].sell = el.children[5].innerHTML;
            }
          });
          setCurrencyRates(DEFAULT_CURRENCY);
        } else {
          throw new Error(result.message);
        }
      })
      .catch((error) => console.log(error.message));
  }, []);