Hello,
I think it depends on your ads categorizing, filtering, size of ads and the amount of ads that fit your website etc… This is totally usual if there is no advert to show on a place. Ads are optimized by Google and displayed on websites, if Google cannot place an appropriate ad in a place, it will be left unfilled. In such cases, it adds the following to the empty ad space. data-ad-status="unfilled". This is targetable with CSS so you can hide the whole ads place if it is unfilled.
This is happening sometimes on your site too. 
I am not sure about the Discourse Ad Plugin Adsense part (I set it up once a while ago, but it no longer run on my website) but I am pretty sure you don’t have to add these URLs to CSP. 
On the plugin’s description it only say add these. 