Website OK on Firefox but not on Safari (kCFErrorDomainCFNetwork error 303) neither Chrome (net::ERR_SPDY_PROTOCOL_ERROR) - google-chrome

Question

Since some days, my website won't load on Safari nor Chrome on Mac OS X (at home nor on my clients computers). It's working well on Firefox (Mac OS & Windows) and IE / Edge, but not Chrome (Windows).
It was well working before that and was not updated since weeks.
I'm facing this error on Safari
Failed to load resource: The operation couldn’t be completed. (kCFErrorDomainCFNetwork error 303.)
And this one on Chrome
Failed to load resource: net::ERR_SPDY_PROTOCOL_ERROR
It seem's to be related to HTTP/2 but I don't really know what is the problem.
I saw that a workaround is to clear the cache and cookie.
I did and it works on Chrome the first time I load the website, but when I navigate to another page, the error appear again.
I also flush opened socket without effects.
On Safari, flushing the cache and cookie has no effects.
My hoster (OVH) tells me that the problem is in my code but I cannot figure out where could be the bug.
Do you have any clue about that ?
Thanks a lot

Answer 1

We have had a problem with nginx and HTTP/2 which resulted in the same error in Safari and a similar error in Internet Explorer.
When we tweaked the nginx buffers to be:
http2_max_field_size 16k;
http2_max_header_size 128k;
the issue was gone.

Answer 2

My problem was disappearing after reloading the page. So it always shows the error on the first load after nginx reload.
Error log shown:
2018/10/21 06:26:54 [crit] 9439#9439: *54 open() "/var/cache/nginx/proxy_temp/2/01/0000000012" failed (13: Permission denied) while reading upstream, client: 37.9.113.93, server: anvileight.com, request: "GET /ar/ HTTP/1.1", upstream: "http://unix:/run/a8/gunicorn.sock:/ar/", host: "anvileight.com"
My problem was that nginx has directive:
user deploy deploy;
and indeed, permissions on that folder were incorrect:
ll /var/cache/nginx/proxy_temp
total 40K
drwx------ 102 www-data www-data 4.0K Jan 6 2018 0
drwx------ 102 www-data www-data 4.0K Jan 6 2018 1
When I changed it to
user www-data www-data;
problem has gone

Answer 3

The problem is a result of Safari holding too much local data for the site in question and failing to deal with that correctly. I use archive.org a lot so I had lots of LocalStorage and Cookie data for that site. The fact that this data is only in my main browser Safari and not in any of my other browsers explains why they could browse the site just fine.
So, the solution:
Go into Safari > Preferences > Privacy
Search for the affected domain name (for me this was "archive.org")
Click Remove
The problem goes away!
Here's a video showing the problem before and after: https://imgur.com/gallery/d1P1FCi

Answer 4

This suddenly started happening for me when the files were referenced on my local in a parent directory. Solution was to move to child directory.