A simulated-audience feature that was dishonest the moment it was visible
Simulated chat existed so the director loop could be developed without an audience. During a real stream it displayed fabricated viewers. That is not a bug in the ordinary sense — the feature worked exactly as written — it is a feature that was fine as a test harness and became a lie the moment it was on screen in front of real people.
It is now off by default and only enabled by an explicit environment flag that no normal launch sets. The general lesson is the one I keep relearning: a development convenience that fabricates data must be structurally impossible to leave on, not merely switched off.