Rift Quest:An Eye For an Eye  

I'm not sure about when Saint Carwin Mathos and War Machine 124-KT fight each other. When the guardians have all of their shadestone collected they summon Saint Carwin Mathos and he fights Gogalab. Once Gogalab has been killed Saint Carwin Mathos usually waits to fight War Machine 124-KT.

The other day the defiants collected their shadestone before the guardians and summoned War Machine 124-KT and killed Gogalab but War Machine 124-KT just despawned after the fight.

Maybe the war machines need to have a specific amount of health after the fight with Gogalab or maybe this only happens every few days.