This is also known as "why are my widgets in the right column being pushed down the page?"

Those positions are where ads appear on sites that do not have an active subscription and have no points through the Crowd Pay widget – most likely, the user seeing this has an ad-blocker enabled in their browser. The frames where the ads appear will remain, but the users would not see the advertisement, thus creating the illusion of an immovable empty space.

There should also be a frame to 'Remove Ads' around each of the ads to make this a little clearer.