I’m not sure if there might be an ‘only’ missing in the antecedent, because otherwise I don’t see why this would follow. Besides, as you note, affirming the consequent does not prove, and need not even probabilify, the antecedent. For it might well be true that only necessary suffering exists, and nevertheless all suffering appears unnecessary. At least this is what @Mijin appeals to when he says that we can take all suffering as evidence against a tri-omni God (because it may be unnecessary).
But then, in a world where all suffering is necessary, and there in fact happens to exist a tri-omni God, this would mean that such ‘evidential’ reasoning ends up supporting the wrong conclusion that God doesn’t exist. This would, of course, be devastating: since that world could well be ours, there would then be just no reason to accept such reasoning as reliable, and hence, the argument can just be thrown out tout court.
This doesn’t follow. Let’s again take Bayesian reasoning as the most widely accepted model of how evidence ought to influence beliefs (some would say, of rationality itself). Then, the probability of A’s innocence I_A, given that we have found A’s fingerprints F_A (on the scene), evaluates to:
Thus, the evidence lowers our confidence that A is innocent, i.e. it is the case that P(I_A|F_A) < P(I_A), where P(I_A) is whatever estimate of A’s innocence we had before, if and only if \frac{P(F_A|I_A)}{P(F_A)} < 1 \Leftrightarrow P(F_A|I_A) < P(F_A). Thus, only if the probability of finding A’s fingerprints on the scene in the case that they’re innocent P(F_A|I_A) is less than the probability of finding A’s fingerprints independently of guilt or innocence P(F_A) do we have grounds to lower our belief in A’s innocence upon finding A’s fingerprints. Merely finding A’s fingerprints on the scene does not give us grounds to believe this. The same analysis works, of course, in the other cases.