Really, what version of the app are you running?  I’m on android and running 8.12.02, and have all my album art present and accounted for.

Odd, my Android is on the latest release and shows no album art.

I'm with OP, no android album art when viewing local files. Can get it if using Plex through the app, but nothing natively 

Latest and greatest like you. Are you sure you're not talking about album art when streaming? You're playing mp3 files on your home network? If so, is your art in folder.jpg or embedded in the mp3? If your music library art really displays properly, I'd like to know more because it has been broken since the new app for me and to my knowledge, many others, and I may have missed it but I haven't seen any announcement that it has been fixed. Do tell more...

Says “soon” here:

https://trello.com/c/WdOoaTMC/59-album-art-for-music-library-android

Well well well. I've been checking the trello from time to time but have only seen the catch-all "music library issues" card; I missed the Android art card under coming soon. Thanks for the info! Fingers crossed. 

Sorry, I guess I misunderstood your situation. My album artwork is there while streaming and also while playing songs that I've downloaded onto my phone. But it sounds like you have a different scenario going on. I hope it gets worked out soon.

The reason is listed here:

https://github.com/amp64/sonosbugtracker/issues/33

Sonos are using the “wrong” api to get the art, they need to do something different on Android. Not rocket science.

Good Lord, based on the length of time this has been outstanding, I thought it was going to require a major architectural rework. I didn't know about your bug tracker, thanks and thanks for doing it. One can only hope Sonos is aware of it.