I certainly experienced this (the vicious try-again cycle) but curious if you have any sources for this?

A person's testimony is a source. I can add mine: you can tell when you're truly blocked because if you click for the accessibility audio-based captcha it will actually tell you you're blocked (but, if you did the visual captcha, would simply loop forever while telling you you did it wrong).

I don't think you'll find an article by Google saying "yes, we sometimes completely block users while making it look like they're not blocked and wasting their time".

That explains why I can never get past Google's captchas! I don't even automate Google searches, I wonder why they don't like me.

Depending on the IP reputation as well as the kind of IP address you have, this can happen.

Google also prefers if you have a Google account logged in.