Caching headers issue on collection

I'm experiencing a weird issue with caching headers on a collection showing the latests news of one of our sites, and I'm not sure of the origin of it:

the collection is not being updated as expected and it's currently showing items from 2 days ago in my browser:

this is what I see when I ping one of the instances of the site directly:

# curl -I localhost:8081/Plone/ultimas-noticias
HTTP/1.1 200 OK
Server: Zope/(2.13.24, python 2.7.12, linux2) ZServer/1.1
Date: Thu, 30 Mar 2017 17:52:23 GMT
Content-Length: 0
Accept-Ranges: none
Last-Modified: Tue, 28 Mar 2017 00:00:39 GMT
Etag: ts70756479.57
X-Cache-Rule: plone.content.itemView
Content-Type: text/html

and this is what I see when I ping it on Varnish:

# curl -I localhost:6081/Plone/ultimas-noticias
HTTP/1.1 200 OK
Server: Zope/(2.13.24, python 2.7.12, linux2) ZServer/1.1
Date: Thu, 30 Mar 2017 17:52:14 GMT
Content-Length: 96320
Content-Language: pt-br
Expires: Mon, 02 Apr 2007 17:52:14 GMT
Vary: X-Anonymous
Last-Modified: Tue, 09 Aug 2016 15:27:59 GMT
X-Ua-Compatible: IE=edge,chrome=1
Cache-Control: max-age=0, s-maxage=300, must-revalidate
X-Cache-Rule: plone.content.folderView
X-Frame-Options: SAMEORIGIN
Content-Type: text/html;charset=utf-8
X-Varnish: 11865642
Age: 0
Via: 1.1 varnish-v4
Accept-Ranges: bytes
Connection: keep-alive

so, I don't know why we ended with X-Cache-Rule: plone.content.folderView if Plone is serving X-Cache-Rule: plone.content.itemView.

this is Plone 4.3.11 with 1.1.11.

and the configuration of Collection is as follows:

I'm using Varnish 4.1.1 and the problem started after upgrading from Varnish 3.0.7.

This does seem like a good place to start, no?

I'm not sure right now; because I had the @@atom.xml view disabled earlier also.

so I don't know it it started when I migrated Varnish or when I enabled syndication.

my main problem here was the cache invalidation; I forgot to migrate the purging part of my previous configuration. I just implemented it again with the information from the Varnish manual:

I hope that will fix it.