Finally got it. I think it was the 30th named kill.
The good news is that the named spawns a LOT.
Trigger all 5 traps and the 5th one you trigger will always be either the named or a placeholder (hunter) that does not corpse-camp or despawn like the young frogs do.
Recommend using a rogue with SoS or a monk or SK with FD to trigger the traps so you dont have to fight a jillion mobs and to maximize churn.
Up the hill behind the static spawn gator near the southern most trap spot is a safe spot to park boxes / groupmates.
Put the fourth young frog on xtar and when he despawns you know the cycle is ready to repeat.