Well, yes, and not a particularly super combination of aircraft type and environment.
Of course that has been addressed in the past, but, [speculation mode] think of car tires that become brittle with the passing of time if not flexed (massaged) and remaining stationary for years on end – how well can deicing boots withstand deterioration by the weather during a very long period unprotected without any use? That combination of external influences just could be a new factor here. [speculation mode off]