Some of my albums in Google Play Music that I listen to on my Android phone have no tracks when I try to listen to them in the Android TV app. It seems to be albums I added myself that are not available in the Play Store, but I can't say for sure.
Is this a known issue?
I know uploaded tunes weren't available right away for Google Home devices, so maybe it's a similar issue. I almost never use the Music app on my Shield. I just cast from my phone instead. Much better UI for picking tracks and I can use my phone as a remote to skip tracks or add new ones to the playlist.