I've tried to get to a contact link in the footer and been hindered by infinite scrolling on more than one occasion. I wouldn't say it happens a lot, but when it does it's frustrating.

I have this happened to me several times but I wouldn't say its frequent, nowadays most sites show 3-4 extra pages then show the "see more" button.

More often then I'd like–anecdotally, about once a month or so.