UPDATE:
So both my wife (Pixel 6a) and I (Pixel 7 Pro) have stayed on owner profiles for a few days and there have been ZERO issues with lagging and screen freeze.
As soon as she went to her "social media" user and back again the issues started again.
However, we discovered that "end session" on the secondary users seems to do the trick.
So, for now, we just have to do without the cross-user notifications, which is OK until a fix comes out.