Cache-Control header which is returned from your origin causing high pings with CDN

I have a CDN provider which undertakes DNS as well as content delivery however when I setup monitoring on all websites the ping is ridiculously high as you can see from the images. I self-host the websites hence the CDN. When I informed them of the pings the indicating its cash control related. I'm not too familiar the with this in-depth configuration so can anyone shine a light on this.

All websites are Wordpress and there are some plugins for CC however when I informed the CDN provider they indicated that I don't need to use plugin e.g. W3 Total cache, etc as I have DNS with them so no need.

they said "Correct, you don't need a CDN plugin as you have a full site integration with DNS. The issue is the private tag in the Cache-Control header which is returned from your origin.

Now I'm at a loss of how to resolve this and ideas, thanks in advance

High Pings on websites via CDN monitoring