I recently noticed that my playlists seemed to be missing on my android phone app. Only a few icons were visible in the playlist category of My Sonos and when I scrolled left no more could be seen. I thought they were gone. I looked on my PC desktop app and all the lists were there.  I discovered by accident that if you tap on the “Playlists  >” category title in My Sonos on the phone you get a full list of all the playlists. My frustration was assuming there was an icon for each list. Hope this helps some searching for their “missing” playlists.