I would assume that software can always fail in the event of a bug in the hardware. That's why systems that are really redundant, for instance flight control computers, have several computers that have to form a consensus of sorts.
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.
