I don't know how it works, but it is very inconsistent.

On mobile right now, I can't scroll past the second post of [1] without getting blocked by an undismissable popup.

If I click on the "read more" button of the first post, I can't scroll down at all before getting that same non-dismissable popup. It makes it hard to read the post itself, because even scrolling a tiny bit (e.g. to get what I'm reading closer to the center of my vision) triggers it.

I've also had other times where I couldn't play a video someone linked to me, but sometimes I can, don't know why.