Why might ssi not work in nginx?

Question

Nginx

Came across strange behavior of Nginx
There is a page with ssi inclusions.
if we send HTML via php-fpm via fastcgi_pass with 200 OK response then ssi instructions are not processed
if we send HTML via apache via proxy_pass with 200 OK response then ssi instructions are not processed
if we send static (.html) via nginx then ssi is processed with errors, when In this case, instructions from HTML are removed,
but if we return a page from Apache with a 404 Not Found response code, then ssi instructions work as they should

Answer 1

config to look at adits ...