Last-modified + nginx + wordpress?

Question

PHP

There is a site on wordpress.
I installed Last modified on it.
It only worked after disabling ssi in nginx.
But it works only on the main page, last modified is not displayed on the internal ones.
Tried different variations of the code and plugins.
Then I removed all the plugins and the code from the site that is responsible for the last modified, on the main page as it was displayed as it is displayed.
What could be the problem? Where to dig?