I had my game as webGL build at itch.io and everything was fine, but now after uploading the new build, I receive the error in the image. I’ve also uploaded the development build and got the error below. Imgur: The magic of the Internet
The error in the second image usually means your server is set to have compression enabled but the (unity) file is uncompressed. I got that error on development builds until I realized (and @Marco-Trivellato confirmed) that development builds are always uncompressed regardless of what you’ve set in the player settings.
So…turn off compression on your server and upload the development build again. Then you can potentially have better information on the original error.