CF does not detect correctly fetched json

The worker fetches the following link: wich returns json data and a application/json header.

The problem is, that Cloudflare does not detect correctly that the feteched data is json, I am referring to your example and just modified it with console.log to understand the detected data type. The opposite script also returns the header:

cf-apo-via: origin,cookie
cf-cache-status: BYPASS
cf-ray: 67c87fc1ec380c5f-SOF
content-encoding: br
content-type: application/json
date: Tue, 10 Aug 2021 10:21:44 GMT
expect-ct: max-age=604800, report-uri=""
nel: {"success_fraction":0,"report_to":"cf-nel","max_age":604800}
report-to: {"endpoints":[{"url":"https:\/\/\/report\/v3?s=BDp9cVf3fJeO4y8YWBdGXEcJrPzzToEV%2BcymjYfH6%2BOg7CUGLPdqerIeOXeafZJTZCZoPEh2IMlOUgemiUNCEnumfmbtyt7sH1jf4hs%2Be8gCaP52urKcz7KnajMhKy8kdg%3D%3D"}],"group":"cf-nel","max_age":604800}
server: cloudflare
vary: Accept-Encoding

with the data:

{"vorname":"Niko","nachname":"Test","email":"[email protected]","plz":"19010","anrede":"Mr"}

In my tests some times it correctly returns json, but mostly it returns just html.

Here is the worker code:

 * Example someHost is set up to take in a JSON request
 * Replace url with the host you wish to send requests to
 * @param {string} someHost the host to send the request to
 * @param {string} url the URL to send the request to
const someHost = ""
const url = someHost + "/user.php"

 * gatherResponse awaits and returns a response body as a string.
 * Use await gatherResponse(..) in an async function to get the response body
 * @param {Response} response
async function gatherResponse(response) {
  const { headers } = response
  const contentType = headers.get("content-type") || ""


  if (contentType.includes("application/json")) {
    return JSON.stringify(await response.json())
  else if (contentType.includes("application/text")) {
    return response.text()
  else if (contentType.includes("text/html")) {
    return response.text()
  else {
    return response.text()

async function handleRequest() {
  const init = {
    headers: {
      "content-type": "application/json;charset=UTF-8",
  const response = await fetch(url, init)
  const results = await gatherResponse(response)


  return new Response(results, init)

addEventListener("fetch", event => {
  return event.respondWith(handleRequest())

Thank you