What's the net::ERR_HTTP2_PROTOCOL_ERROR about?

In my case it was - no disk space left on the web server.

For several weeks I was also annoyed by this "bug":

net :: ERR_HTTP2_PROTOCOL_ERROR 200

In my case, it occurred on images generated by PHP.

It was at header() level, and on this one in particular:

header ('Content-Length:'. Filesize($cache_file));

It did obviously not return the exact size, so I deleted it and everything works fine now.

So Chrome checks the accuracy of the data transmitted via the headers, and if it does not correspond, it fails.

EDIT

I found why content-length via filesize was being miscalculated: the GZIP compression is active on the PHP files, so excluding the file in question will fix the problem. Put this code in the .htaccess:

SetEnvIfNoCase Request_URI ^ / thumb.php no-gzip -vary

It works and we keep the header Content-length.

I am finally able to solve this error after researching some things I thought is causing the error for 24 errors. I visited all the pages across the web. And I am happy to say that I have found the solution. If you are using NGINX, then set gzip to off and add proxy_max_temp_file_size 0; in the server block like I have shown below.

 server {
  ...
  ...
  gzip off;
  proxy_max_temp_file_size 0;
  location / {
    proxy_pass http://127.0.0.1:3000/;
  ....

Why? Because what actually happening was all the contents were being compressed twice and we don't want that, right?!