I'm serving my WordPress on a subfolder of a node.js app. My WordPress URL looks like

Everything runs well except when I try to set the fast_cgi_cache.

Here is my configuration:

location @blog {
    rewrite ^/blog/(.*) /blog/index.php?q=$1;
  }

location ^~ /blog {
    alias /var/www/blog;
    index index.php;
    try_files $uri @blog;
    
    # Caching
    set $skip_cache 0;

       # Don't use the cache for logged in users or recent commenters
    if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_no_cache|wordpress_logged_in") {
      set $skip_cache 1;
    }

    # POST requests and urls with a query string should always go to PHP
    if ($request_method = POST) {
            set $skip_cache 1;
    }
    if ($query_string != "") {
      set $skip_cache 1;
    }

    # Don't cache uris containing the following segments
    if ($request_uri ~* "(/wp-admin/|/xmlrpc.php|/wp-(app|cron|login|register|mail).php|wp-.*.php|/feed/|index.php|wp-comments-popup.php|wp-links-opml.php|wp-locations.php|sitemap(_index)?.xml|[a-z0-9_-]+-sitemap([0-9]+)?.xml)") {
      set $skip_cache 1;
    }
    #end Caching


    location ~ \.php$ {
    include fastcgi_params;
    fastcgi_pass php7-fpm-sock;
    fastcgi_cache_key "$scheme$request_method$host$request_uri";
    fastcgi_split_path_info ^/blog(.+\.php)(/.*)$;
    fastcgi_param SCRIPT_FILENAME $request_filename;
    fastcgi_cache WORDPRESS;
    fastcgi_cache_bypass 1;
    fastcgi_no_cache 1;
    fastcgi_cache_valid 200 301 302 60m;
    fastcgi_cache_use_stale error timeout updating invalid_header http_500 http_503;
    fastcgi_cache_min_uses 1;
    fastcgi_cache_lock on;
    fastcgi_pass_header Set-Cookie;
    fastcgi_pass_header Cookie;
    fastcgi_ignore_headers Cache-Control Expires Set-Cookie;
    add_header X-FastCGI-Cache $skip_cache;
    }
}

Now when I log in and visit a page like: I get an error: /var/www/blog/2020/14/some-slug/index.php doesn't exist.

This happens only when I'm logged in. i.e This test is true:

$http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_no_cache|wordpress_logged_in"

How can I fix this issue and can you please explain why it's happening? Thank you.