There was nothing folded in the mind maps. I’ve never changed the font in MN (well, once when I first got it but they were all equally boring so I never changed them). All my mind maps have the same fonts and some of them show up, some of them don’t during a Note search with any word.
Edit: okay, there seem to be TWO circumstances when empty results are shown in the search.
The node itself has no title (in this case it should show the start of the first batch of notes on the node)
The node has a long title (these titles aren’t particularly long, they don’t push the boundaries of the field, but it seems to be more than five or six words causes the result to be empty)
Of those 3, Avenir Next is the only acceptable one for work and lo and behold, it does appear to solve the issue. Hopefully, now that the source of the problem has been narrowed down we will see a fix eventually.