In our production environment I regularly see functionality magically appear and then dissapear weeks later. I have no idea why they come and where they go.
Some I know are things like "Record via Loom" button appeared at one instance, or "create comment at a previous date/time" which worries me from a governance perspective or "AI features" available a while ago and then gone again.
Interestingly I'm seeing these pop up in our production environment before our sandbox, which you'd imagine should be the other way around.