It doesn't even need a bug in the hardware; cosmic rays or alpha particles can also cause the same type of issue. For those, making systems redundant is indeed a good solution.
For the situation of an actual (consistent) hardware bug, redundancy wouldn't help… the redundant system would have the same bug. Redundancy only helps for random-style issues. (Which, to be fair, the one we're talking about here seems to be.)
That's why some redundant systems use alternative implementations for the parallel paths. Less likely that a hardware bug will manifest the same way in all implementations.
For the situation of an actual (consistent) hardware bug, redundancy wouldn't help… the redundant system would have the same bug. Redundancy only helps for random-style issues. (Which, to be fair, the one we're talking about here seems to be.)