The way you described it looks like you have an issue with url-map because you can access the http version of your site.
To be absolutely sure double check (or create new) url-map with gcloud command:
gcloud compute url-maps describe web-map-http
This has nothing to do with the packet length. Based on the small portion of the packet capture you show there are simply lost packets. The last sequence received was 65793 and then the next packet in the capture starts with 67956. That's why it is repeatedly acknowledging sequence 65793. The server should realize this after a while and resend the missing ...
Why don't you run your own?
For httpbin.org, the source code is available on GitHub and it's also available on Docker:
docker pull kennethreitz/httpbin
docker run -p 80:80 kennethreitz/httpbin
See http://httpbin.org for more information.
Also, you could achieve what you ask for i.e. "presented somehow" e.g. with a PHP one-liner:
I had an accidental "http2" directive on one of my port 80 server directives (you can see it in the "api" server). For some reason using this on one server block affects others. Thanks to Michael for the hint. For anyone else experiencing the issue, removing "http2" from all of your port 80 servers fixes the issue.
I don't know if this will help some people, because i got the same problem when i was setting up my wordpress and couldn't get around the problem. This was very annoying to me but i remember that i sucessfully configured without any problems once.
Whoever with researching and trying stuff to see what went wrong i've tried to configure the wp-config.php to ...