after reading your comments on the autothrottle, I remember when in the 320sim , you have to "recycle" the throttle, or you have no power.
I don't have any experience on the 320 except some hours in the sim, ... to kick a computer to react (an important one),you must move the throttle handle all way back .is that safe?
I can not say at what stage of the flight, we got this "simulation"or if it was a sim problem, but our instructor told us to recycle the power...