I camped this rare while leveling in Terminus and this is the info I found:
Level 3
Killed at 8:38 pm EST
Spawned at 8:43 pm EST
Killed at 8:43 pm EST
Spawned at 8:48 pm EST
It appeared to have a 5 min respawn timer and no other adds came with it. There were several Spectral Harvesters and Endless Dominators around it and would randomly attack them. It walked around in a small area so no threat of aggro unless you get too close.
I received the Scavenged Construct Plate each time and I did not have any other competition.
One strange thing I noticed is after the Raging spawned several times a Forgotten Warmachine spawned 5 times+ at 5 min intervals. I don't know if the Forgotten is a placeholder for the Raging or not but it had me intrigued.
Good luck
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