I have some perfectly straight arrows that will not fly worth a crap. I am sure others have experienced this. I am pretty sure this is not possible. It seems likely that the arrow has a slight bend in it. Metal fatigue in aluminum can indeed be introduced with repeated flexing.
Arrows undergo more than slight flexing when released from a speed bow.
I am not the first to experience this phenomenon as it was pointed out to me by more than one fellow shooter. To date, however, no one has given a definitive answer as to why. You can quit looking for the answer, you've just stated it yourself. Aluminum can fatique with repeated cycling. I'm no expert in metalurgy, but it seems to me that this would cause loss of spine.