Started a bullet game and couldn't see the knights for either side at all. Pretty sure this isn't a setting so I assume it's some sort of bug.
I had the exact same thing for queens. it was persistent from game to game (also on the captcha!) and i was working on a laptop (not the app). After i closed the browser and restarted lichess, it was fixed:
lichess.org/forum/lichess-feedback/invisible-piece-in-lichess-gamesSame for me with my other account I couldn't see my king