I noticed this once a couple weeks ago. While I was viewing in private mode, the page flashed the usual page of recommendations, and then promptly removed them all with the message "Search to get started!"
YouTube is just taking a page from all the social media giants, and heading in the direction of a gated community. For some idiotic reason, more and more sites on the web are blocking you from accessing content unless you sign up. Gone are the days when you needed an account to participate, now you need one just to observer. Yeah, you might think I'm overreacting as usual, but we really are heading towards a society where there is no public access to content, despite everything being available on free accounts paid for with advertisements. I shouldn't need to have 200+ accounts all over the web just to "surf".
I see this as a very bad thing, as it implies that the only content you can see is the stuff that's been "tailored" just for your preferences. Sometimes, I want to see the same content that everyone else does, just for a bit of perspective. I don't want to be trapped in a bubble, and certainly not the bubble the marketeers want. I think it's kind of sad how people say this is a good thing, whether they're being sarcastic or not. It is NOT good to build an infrastructure so that everybody is treated differently by default, and you're not allowed to know what kind of content other people are watching. It should always be possible to view baseline content. But, again, we don't live in that world anymore. So much for the information superhighway and the accessibility of information to everyone.