Doryani Not Dropping Life Remnants When Hit

In the second phase of the Doryani fight, the mech does not drop Life Remnants when hit, as per the Sanguimancy perk.

It could be that he's immune to crits, but that would make him the only enemy I've encountered like this so far. I tried breaking his armor to see if that made a difference. I suspect they are dropping inside him and getting stuck, but his hit box is too big for me to enter pickup range even if I roll into him. He can move around sometimes but I haven't seen a remnant yet.

Whatever the case, it makes for an extremely difficult time because I have no way to use skills without precious life remnants, as Sanguimancy adds a life cost to everything....