Yeah, reverb has been broken on Mac for a while. You’d be surprised to know that a reverb instance was created for each source… aka a default of 32!
Fixing this obvious performance issue would unfortunately require a significant rewrite of the mac implementation so we decided to disable it since we were rewriting the entire mac platform back end anyway.
Feel free to re-enable it by setting CORE_AUDIO_REVERB_ENABLED to 1. But I guarantee your mac performance will not be good.
Incidentally, the mac backend for the new Unreal Audio Engine was just completed this week.