I was typing and about to post something when suddenly my screen scrolls down to the bottom of the page. I was forced to watch an ad! If I scrolled up, it would go down again. It even asked for permission to use my location! What the heck!
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Just happened to me too. I'm using Google Chrome. It appeared to be a KaiserPermanente ad playing in the 2x2 grid of ads in the bottom of the page. I couldn't use "Back" on the browser or click any links as it would just jump me back down to the ad. Had to close the tab and come back into the site from the front.
It started with a flag that popped up at the top of the my browser asking to share my location. I said 'block', and then the screen jumped down to the ad.