iTunes playlists folders don't show anything

So suddenly today, many of my playlist folders are like this: "No items..." and yet, there is a playlist within that folder. When I select that playlist...

Yup. The playlist is in the folder.

I can "fix" this by making any change to the folder; eg, move a playlist out of the folder, then it works fine (and continues to be fine after returning the playlist.)

I restarted the computer twice; that didn't fix it.

I went back to my saved iTunes library. That fixed this problem – but all my "View as" settings were back to Playlist after I'd reset them to "Albums" after 12.4 screwed that up.

This is the worst version of iTunes ever.

(And why doesn't command-click close all folders which, for some reason, are now set to be exposed?)