stuckgear;
Stall recover and enter a second stall in under 30 seconds, in an A321?
I agree with your implied conclusion...no, I don't think this is a stall/secondary stall. We might say this could be "spurious data"...
tubby linton;
Obviously this will not be as accurate as the fdr data,
No, and we don't know how FL24 creates the vertical speed data. If it is derived from P.Alt then it is only as good as the P.Alt parameter. A typical data frame on an A321 will have both inertial, recorded and perhaps GPS VSI parameters, (older data frames such as those installed on the B737 Classics derive vertical speed from P.Alt).
. . . but it does show trends of what may have happened.
It may or may not, depending upon other, corroborating parameters which FL24 is incapable of presenting because ADSB doesn't have them. I would like to know what the cabin pressure and cabin rate-of-climb parameters have to say, for example.