I also have problems sharing with my wife (Premium to Personal).
I have shared a document back in 2017 and it still works, but the new notes and notebooks I have shared with her, does not show up. Det does get the emails, but when clicking on the button, only the old not is visible.
I have been a happy user of Evernote for 12 years, but this has made me look more into using OneNote or investing in Notion 😞
Work chat work, when it's unitiated from her account (and shows up with the correct email-adress).
I can answer, but when I try to start a new chat it does not show up on her account.