My view of the events
First the facts, as they appear in the report :
They performed the planned (?) low speed test, involving an entry - and an immediate exit from - into α floor.
The altitude for the test is lower than the recommended FL120-140 by all documents
In this exercise, they expected to see successively Vls, Vmin, α prot and α floor, marked by an automatic trigger of TOGA thrust. They even talked about the ATHR handling at that point ( "push, disengage, reengage" )
They never saw that succession of events... Instead, they had a "stall warning" (we can safely assume that it was the "STALL...STALL" call-out and not the "SPEED...SPEED" one would get in normal law.
They selected a manual TOGA thrust and then,
They experienced some difficulty with the flight path control, ending in a plunge into the sea.
In the report there are two major issues that the investigators have not commented upon but just mentioned as "in passing" :
The frozen -"frozen" as in "not moving due to a blockage" of any sort - AoA sensors, probably feeding the FACs erroneous data critical to the speed limits info displayed and the computation of the AoA protection speeds.
As the print-out shows the AoA1 and 2 unmoving parameters, one can also assume that the stall warnings came from the - unrecorded - stby AoA.
The stabilizer (THS) was automatically - and correctly, in view of the deceleration - trimmed to max nose-up and stayed at that value for the remainder of the flight.
On this subject, in "Normal Law", the auto-trim stops when the airplane enters an α prot situation...and in "Direct Pitch Law" it is unavailable, the crew is reminded by a message urging them to use the manual trim wheel.
But, because of the unavailable AoA data, they never entered α prot and got instead a stall warning
They did enter the "Direct Pitch " mode because of the landing gear been extended... and yet, the stabiliser still showed no movement : jammed or un-utilised ?
That un-moving stabilizer, stuck at max nose-up (for want of another word) couldn't be overcome by the full nose-down demand by the PF, especially when one considers the not-so-light pitch-up moment that the engines at TOGA thrust would induce.. In other words, the sidestick authority in pitch wasn't enough to check the increasing pitch attitude of the airplane, leading to the two subsequent successive stalls.
I have left out all the reversions that could have occurred during that maneuver, because in my opinion, they all lead to a further complication of the crew situational awareness.
Because in the end, I believe that they entered a totally unexpected situation they were not either prepared or trained for, with major handling difficulties and, in my opinion, some disorientation...
A situation that was unrecoverable so close to the sea.