Question Animation rigging with Two-Bones IK collapses character body

I'm adding animation rigging to my character so the player can move head/hands which should affect the body but continue to play different animations (idle, run, etc). I've added Two Bone IK for hands and the head and also calculated the legs IK with a script to properly bend knees and rotate the foot. Everything works as expected until the player starts to move head down (Target from the Two Bone IK component, linked to the Head bone):

I want the character to bend knees when a player moves his head down.
What did I miss in my IK setup?