It could be the search requires more of an "exact match" with the search phrase.
For some reason, Sicilian isn't spelled exactly how it sounds and only has the one "l" and you might try the apostrophe after the "n" in Queen's gambit. That's the only thing I can think of right off hand. It seems to work for me when I use those search terms. Like me, I would easily know what you're talking about just by the context, but some of these search engines can be sticklers on spelling if they require an exact match search. (This is just my guess.)
As far as the series go, sometimes you can "search by author" and look for the series. Of course, that might only be helpful if you already know it's a particular author who did the series. Usually if you get one of the videos in the series, it will have a link to at least one other video in the series as a "related link", but I'm sure you already knew that.
In my copy of Chess Life this month, I noticed Chess.com was featured first in best sources for chess instruction.
If my memory serves me correctly, you had mentioned you were interested in studying the Najdorf variation of the Sicilian.
Well, in that same article, the author mentioned GM Sam Shankland's video series on the Najdorf from back in '09. Thought you would probably want to know about it considering your posts.
I wish I knew some secret hack or trick to finding the series and openings, but that's about all I know on it.
Maybe someone else can post a better way here and that way others who may be looking for a better way to search the database (besides just you and me) will also be able to read it and make use of it.
When I go to the video section of this website and put an opening like Queens Gambit or Sicillian in the "search" field, I get a response no videos found. Can someone please explain the correct way to find these type of videos without having to click on each GM and go through every page to find specific videos. Also, is there anyway to search for a video series, which I happen to like because you may get 5 videos by a GM on the same topic. thxs