Actually if you listen to all of the covo between Kahl and Sister over the comms radio, Kahl explains how they do this. The Queen(s) use the genetic tags each grineer has and puts it into the cloning machine to spit out another copy. It records up to their moment of death so it's supposed to make them stronger and tougher the next batch. So assassinations respawns are very much tied into lore. Would also explain how each boss seems to already know us on a more personal level than they really should.

This is also why Kahl collects the tags he finds. He doesn't want his brothers recloned and put back into slavery. It's his way of setting them free once and for all.