Where would you start with gradual pickup drift? (tray-to-fixture transfer)

We keep nudging pickup points when our Fairino FR5 setup gets unreliable at tray-to-fixture transfer with a machined aluminum puck in a compact parts transfer workshop. The tray looks like it's in the same place, but the grip seems less square. I'm suspicious of all these tweaks. What should I inspect before blaming the arm or reteaching everything?