I've done this a bunch and it's a constant problem. When the final boss shows up after getting the Heroic Event message, you fight waves and waves and waves and waves and waves of adds but can't damage the boss. The glowing enemies that drop the Harmony orbs never show up. The last time I played this glitch prevented the participants from collecting rewards. At least one person I know didn't even see a chest at the end. And he was waiting at the chest area as everyone came to claim. This is clearly in need of a patch. This is ridiculous.