It seems Optimus Prime and Elita One have no idea that Alpha Trion re-built them after Megatron destroyed them, as revealed in War Dawn (1985). Though nine million years passed since then, it is unlikely they could have forgotten thing like this.
As Starscream brags about how he managed to capture Prime, the animation of the scene is completely missing. Optimus should be hanging down from a rope above a pool of acid, yet the pool and its contents are missing, thus the bubbles and smoke seemingly rise up from nothing. Also, both the bubbles and the smoke are unmoving.
As Alpha Trion says "It's your turn to help her.", Optimus Prime's mouthplate is moving.