In Apple Music streaming (no local files), I can find and play a song, but once added to a playlist it displays a dotted line cloud and will no longer play. This is true for Apple Music in-app, in-browser, and in-browser not signed in (can find and play but can't test playlist without being signed in). What is causing this behavior? It's not every song, but many, and not just this album.
Examples below are from a M5 Max Macbook Pro (26.7.1), and iPhone 12 Pro Max (26.6.2)
not playing from playlist in Music:
playing from a search in-browser:
no longer playing once added to playlist in-browser (no dotted cloud in browser):
playing from search in phone:
no longer playing on phone once added to playlist: