Could it be an erroneusly low airspeed in all ADRs such that the airplane was actually deep in the overspeed and then the APs disconnected and the pilot carried out unreliable speed procedure memory item when above 10,000 ft: pitch 5º, climb thrust.
What was the pitch and AoA at the time of the AP disconnection? I think that is a critical information. is it available?
if these were low, that scenario would explain the pitch up input, and such a sudden and large pitch change (say almost 5º) at that level and speed (overspeed) would make possible a very large lift increment and climb rate. but I am not sure that a stall could result from this.
we will have to wait.