XF 2.1 css.php not returning text for most first views

[Marcus]

I have the issue (xf latest beta) that for first (several) views css.php does not return any text, so the webpage isn't really pretty for the first views. Until once css.php works, from that point on web pages are pretty again (because the css is saved in the browser).

I have activated and deactivated general cache in config.php, its always the same. Is this a very known issue (with an easy fix)? Seems to be my server, but where is the problem? Thanks!

one of the css.php which doesn't reply anythin for the first views.
css.php?css=public%3Anode_list.less%2Cpublic%3Anotices.less%2Cpublic%3Aextra.less&s=42&l=5&d=1546496444&k=a573230aa7b4bb947598d7a86ee74eccefa707c5

Header
Accept: text/css, /; q=0.1
Accept-Encoding: gzip, deflate, br
Accept-Language: de-DE
Cache-Control: no-cache
Cookie: xf_csrf=JHCPJpIy3SosSBI-
DNT: 1
Host: www....
Referer: https://www.....
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.140 Safari/537.36 Edge/18.17763

Header Replied
cache-control: public
content-encoding: gzip
content-type: text/css; charset=utf-8
date: Mon, 07 Jan 2019 17:45:39 GMT
expires: Tue, 07 Jan 2020 17:45:39 GMT
last-modified: Thu, 03 Jan 2019 06:20:44 GMT
server: nginx/1.12.2
vary: Accept-Encoding
x-frame-options: SAMEORIGIN
x-powered-by: PHP/7.2.11

 

[Marcus]

It sure wasn't xenforo as I guessed: It helped to setup a complete new server with new ssl certificates and a complete new basic web server configuration. As long with upgrade to the latest xenforo beta.