Ever since sites started doing this, StackExchange has been the one constant thorn in my side. "We'll only ask you once" and yet that popup has appeared every single time I have visited the site, and I'm there quite frequently for programming questions. Other sites like StackOverflow were able to store a cookie containing my selected preferences, but SE seems to ignore my selection and I finally gave up even trying to click on the banner years ago.
Funny thing is, I checked them again after reading this article, and suddenly there is no cookie banner on the page. Hopefully they finally got it fixed and this isn't just some temporary fluke.
I've been running uBlock Origin forever, didn't even know reddit had ads until people started complaining, but it's never done anything for these stupid cookie warnings.