CORS error when sending many post requests using a loop in React

Questions and Answers Strapi Backend
1
System Information
  • Strapi Version: 3.6.3
  • Operating System:
  • Database:
  • Node Version:
  • NPM Version:
  • Yarn Version:

Hi!

When I’m using a loop to send many post requests in production, then some of them will give this error:
Access to XMLHttpRequest at 'https://api.domain.com/items' from origin 'https://app.domain.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

Others will be successful. I have CORS origin in strapi config and I can send post requests, but when using a loop then sometimes it fails.

for(let i = 0; i < file.length; i++){
const data = {
    name: file[i]["Name"],
    number: file[i]["Number"],
    category: category[0].value,
    creator: auth.user.id
}

let productPhotoFromFile = Array.from(productPhotos).filter(obj => {
    return obj.name === file[i]["Photo"];
});

const formData = new FormData();

if (productPhotoFromFile.length > 0) {
    formData.append("files.photo", productPhotoFromFile[0].originFileObj);
} else {
    const blob = await (await fetch(unknownPhoto)).blob();
    formData.append("files.photo", blob);
}
        
formData.append("data", JSON.stringify(data));
try {
    await axios.post(process.env.REACT_APP_API_URL + '/items', formData, {withCredentials: true});
} catch (error) {
    console.log(error);
} 
}

I can’t see anything in Strapi console and on localhost I don’t have this problem. Can’t understand what is causing this?