Can't refresh genius playlists in iTunes

Hi,

I have iTunes 12.2.1.16 and a 160GB iPod classic, and a lot of Genius playlists in my iTunes library (some created in the application, some on my iPod, if that's relevant). On a couple of recent occasions, I've synced my iPod and the Genius playlists in iTunes have become corrupted or something: they still have the spinning atom icon beside them and appear at the top of the pile in the source sidebar, but the Refresh option that usually appears in the banner above the playlist is absent and when they're copied across to my iPod, they're just normal, non-Genius playlists indicated with a musical note icon sitting at the bottom of the list. This never happened prior to iTunes 12 but has persisted in the latest two revisions.

Has anyone else experienced this and does anyone know how to avoid this happening? If there's a quick way to re-Genius-ify the playlists, that'd be great as well; recreating them individually for the seed song takes ages.

Thanks for your help.