On mw.org now, since today's deployment:
The icons for the watch stars are missing from the topic header, as well as the icons for the side rail.
On Chrome, if you click the star to subscribe to a post, you get the no-JS version, which takes you to a separate page and then dumps you on a "This has been added to your watchlist" page.
On Firefox, you can still click the blank icon to subscribe & unsubscribe from a topic.
I'm putting this in the current sprint, because the Chrome subscribe/unsubscribe experience is really annoying.
See also T99873: Wrong star icons. The difference is that shows an icon, but the wrong one.