I think I am doing everything correctly. I added the tag "Humility" to my sermon in the info pane, and am searching Docs for mytag:Humility. Notebooks with that tag show up, but the sermon does not. The sermon shows up if I search for a phrase from it, so it is indexing correctly.
Interestingly, when I went to add "Humility" to my sermon, it showed it as a new tag (even though I have used it before in Notes), so are the sermon tags being processed differently than the notes tags for some reason?
I am on beta, but I don't think that is relevant.