I forgot to set the "Remove at Battle End" tag on the Rare Treat. Oops.
Aha, I see the problem: I set the wrong element ID in the shield's state, so it wasn't amplifying the Gravity Amp effect. (It should work like Elemental Amp effects; 700 against Aeternator should become 875 with the next patch, which will be particularly good for a certain task.)
I'll patch that issue with the Point Research and Regen Healing- probably will have more time for that a bit later today.