In Patch 10.0.7 on NA servers, the third boss of Temple of the Jade Serpent is bugged and remains active in the final phase of the encounter. With 10.0.7 now live on NA servers, players need to be careful about running Temple of the Jade Serpent keystones as the 3rd boss is bugged and much more deadly than before.
During the final phase of the encounter, the boss is supposed to despawn and be replaced by Yu'lon. However, currently the boss doesn't despawn and remains untargetable, casting the deadly Jade Serpent Strike, absorbing a large of healing and dealing high damage to your tank.
Read more on wowhead.com