When you hover the mouse over a username or avatar icon as a logged-in user, you see a profile card; and when you click on it, you end up on the profile page. Neither action has any effect when you are not logged in. When opening the profile manually, it redirects to the login page, so I presume this is somewhat intentional; but clicks should also redirect there, and IMO the profile card should still be shown if possible (it contains very limited information compared to the full profile).
This is a consequence of this change we made in the settings:
Surely an unintended one, though? If the user clicks an interface element which has explicit UX hints for being clickable, there should be some kind of feedback.