Dozy..
I'm not sure if human/machine cognitive overload is the problem here so much as the level of pressure and stress on the PNF. For all my opinion's worth as a layman with an interest, could it be the human/human interface that is causing the issue?
I think there is a mix of overload impacts that affect each crew member differently.
First there is what is called the 'classic inverted U curve (Yerkes and Dodson 1908) which balances arousal and performance. The crew were at the lowest point for attention and arousal at 2am in a relatively boring and benign cockpit environment. This is the worst level of attention and alertness the bottom of the inverted U and poor performance. Ideally, the crew need to be engaged so that their arousal/attention is at the top of the curve of the inverted U and performance is best. However, instead, what happened was a sudden burst of emergency activity both mentally and physically demanding with instruments and techniques routinely used in Normal Law not working. Learned sim ride behaviors seemed to make things worse. This moved the PF at least, right to the other end of the Inverted U where the level of arousal was so high that performance drops off. At that level the cognitive overload that we had discussed could lead to 'attentional tunneling' (or cognitive tunneling) where the PF concentrates on a few aspects of the task and is not conscious of anything outside those aspects.
The PNF has a similar jump to the wrong side of the U but as you state has a problem as he finds that what he says is not being listened to. This is probably due to the PF attentional tunneling, but PNF may think that it is some lack of authority on his part - the authority gradient. He may also be aware that he is overloaded with all the various aural verbal analysis, visual verbal analysis trying to read ECAM listen see what PF is doing now. So PNF wants the captain back. It is noticeable, that PNF is
not making it plain shouting that
the aircraft has stalled get the >deleted< nose down!! - no, PNF is muttering about the delay getting the captain.
When the captain does arrive, instead of a peaceful cockpit that he left, it is a cacophony of alerts and wind noise. PF is 'making mayonnaise' with the SS and presumably staring fixedly at the instruments. I did not see any transcript of a succinct briefing from PNF to the captain giving an order of events detailing the problems - only the captain being asked what did he think is going on? Was the captain even told that the aircraft was in Alternate Law? (is it immediately obvious if you are not told?) Would the captain have identified the stall if he had just a three sentence briefing on events?
I have said elsewhere that this turned into a human factors nightmare. Books will be written about this incident. Procedures and training both live and simulated will be changed I hope for the better.