What is the point going into the chambers more than once for the mission?
They drop nothing and have no trove or chest.
Am I missing something?
I think so. 
Although I do not know, if their trove is only a one-shot chest.
Well, there is the Drecree of Malmouth Scepter, if you think it’s good for your build.
Ahh, i had a suspicion for a little while that they were the ones who dropped that. Thanks for confirmation.
Grim Tools FTW - in this case you just need to know who Dreven Cole is, or where he spawns
Just tried with another character on ultimate. On the mission there is a chest at the back of the room. Was just an Heroic chest which dropped 2 greens not like a real boss one shot chest which are called exalted? I didn’t check to see if it could be opened before killing them.
I did get a Legendary as a mission reward.
Went back again and no chest so as it stands farming the Decree of Malmouth is the only reason anyone would want to go in there a second time.
No worries, I recently found another secret for the first time, which has been around for about 1 1/2 years.