We have multiple smart devices and Google Assistant smart speakers (Sonos One, Nest Mini, Nest Hub).
Both me and my partner can control devices around the home but she can't add items to our shopping list. The shopping list is in Google Keep and the note is shared with both of our google accounts. Both our voices are Voice Matched and Google Keep has been selected as the note service.
When she tries to add an item to the list, Google responds "I couldn't verify your voice, so I can't change any lists. You can either try again, or verify your voice match settings in the Google Home app."
Would you mind running a quick test for me? I want to see for sure if this is only happening with Google Keep or across all account-related apps. Could you use the voice command to play a song on YouTube and then check to see if it shows up in your account history or your partner's history? Then repeat the test with your partner playing the music. If the history is only showing on a single account, we can know that the problem is on the account level and not the app level. Let me know if you're able to test that out.
Sorry, been super busy so hadn't had time to test this.
So to test it I had to remove my Kitchen Sonos speaker as the default (as I don't have my Sonos linked with YouTube Music).