Nginx not caching when Vary headers not being ignored

First off: I don't have much experience with Nginx.

I'll just proceed directly to the problem though:

Nginx config:

user www-data;
worker_processes auto;
pid /run/nginx.pid;
events {
worker_connections 2048;
multi_accept on;
}
http {
proxy_cache_path /var/nginx_cache levels=1:2 keys_zone=STATIC:10m inactive=24h max_size=10g;

upstream server {
server -removed-;
}

server {
listen 80;
server_name -removed-;
location / {
gzip on;
gzip_disable "MSIE [1-6]\.(?!.*SV1)";
gzip_http_version 1.1;
gzip_min_length 500;
gzip_vary on;
gzip_proxied any;
gzip_types
application/atom+xml
application/javascript
application/json
application/ld+json
application/manifest+json
application/rss+xml
application/vnd.geo+json
application/vnd.ms-fontobject
application/x-font-ttf
application/x-web-app-manifest+json
application/xhtml+xml
application/xml
font/opentype
image/bmp
image/svg+xml
image/x-icon
text/cache-manifest
text/css
text/plain
text/vcard
text/vnd.rim.location.xloc
text/vtt
text/x-component
text/x-cross-domain-policy
text/js
text/xml
text/javascript;


add_header X-Cache-Status $upstream_cache_status;
proxy_cache STATIC;
proxy_set_header Host $host;

----> proxy_ignore_headers Vary; <-----

proxy_cache_key $host$uri$is_args$args;
proxy_cache_use_stale error timeout http_500 http_502 http_503 http_504;
proxy_pass -removed-;

}



}
}

When the line 'proxy_ignore_headers Vary;' is set, everything will cache, including the HTML pages. When I remove this line, everything gets cached EXCEPT the HTML pages. Why is this?

I would like that Nginx caches the HTML pages even when Vary-headers are being sent by the origin server.

I hope someone can help me :).

Response Headers are:

Vary:Host, Content-Language, Content-Type, Content-Encoding