The If-Modified-Since check fails. How to overcome?

Question

linux

There is a web server on Debian Jessie with a bunch of Nginx + PHP7-FPM + MariaDB 10, where a WordPress blog is spinning. Using the checker, If-Modified-Since decided to check the correctness of the site response, however, the service reports that the site did not respond to If-Modified-Since and thus 304 Not Modified not found:

Please tell me what steps can be taken in Nginx \PHP\Wordpress to get verified? How to poke his nose? Because the developer tools in Mozilla Firefox perfectly send If-Modified-Since to the site and correctly receive 304 Not Modified:

Answer 1

https://forum.nginx.org/read.php?21,251834,251844#msg-251844 _

Answer 2

Is it possible to close this issue with the implementation of Leverage Browser Caching? https://varvy.com/pagespeed/leverage-browser-cachi...
Look here there is a solution for nginx.conf