The issue is if two Spotify accounts are linked on the same device, one Premium and one Free, the Google Home will share privileges of the Premium account even if the Free user initiates a music command, and this will in effect 'use' the premium user's account once the command goes through.
For example, Spotify Free accounts can only play free radio stations inspired by a requested song/album/artist/playlist. However, when a Spotify Premium account is also linked to the same Google Home, the Free user can request any song/album/artist/playlist directly, as if the Premium user requested it using their subscription. This creates problems though, since if a Free user requests Premium content on a Google Home with both account types linked, it assumes the Premium user's identity even if they could be listening to music elsewhere in the house, cutting them off. This is contrary to the expected behaviour of only using the Spotify account belonging to that user's recognized voice model. Right now, Spotify Connect properly separates accounts when requesting non-premium content, but it messes up once a Free user requests Premium content in this way.
If I initiate a music command, I want it to attempt to play using my Spotify Premium account only. If a non-premium user attempts to play premium content, it should attempt it via their Spotify Free account, and fall back to radio stations if all-access is unavailable. It should NOT share the privileges of the higher account and assume identities on Google Home just because two accounts are linked to the same Home device. Hope this is clear and it gets changed/fixed. Thanks!