Vagan Unkillable in Research Safehouse

I Ran a Research safehouse with Vagan as a subordinate (ie. not the leader). I killed the leader (Janus, as leader, in this case), then attempted to kill Vagan. After getting his health to zero according to his health bar, he did not die. This persisted for a couple of minutes, until he eventually perished.

Not sure if this is important, but I also had a Kineticist Merc with me.

for certain betrayal members in safehouses (Vagan and Hillock i can think of) you have to let them perform a jump attack at you before they can be killed. You can keep your distance from them to bait this attack out. Try not to permanently freeze them to let them attack you.

Hope this helps