It seems the challenge was a bit much for the dungeons themselves, as Challenge Dungeons are having some issues that caused Blizzard to disable them while they work on a fix. Players may get kicked out during their run as the process takes place.
We’re aware of and investigating issues with Challenge Mode Dungeons, and we’re disabling them while we do so.
Players may find themselves kicked out of dungeons due to this disabling step.
Thank you for your patience and understanding.