I don't get it...I have it in my quick-slots...I choose it during the fight...I press the "use item" button...and all it does is shooting the blue energy bolt. It is not placed...
You don't have to put it in the quick slot etc. When you fight the kayran, there will be a spot with yellow highlight, you then need to LMB to set the trap. That being said, my trap missed and it disappeared. Wth.
It didn't disappear, most likely. I found that, when deployed, it stops glowing and is rather hard to see. Your next thought my be to wonder why it didn't grab the tentacle, then. When I used it, I still had to stand next to it and roll away.
I could be totally mistaken. That is just how it seemed to play out to me.