Only the chance to attempt switching the volley to another target is guaranteed, but there are a number of other requirements to be met, too, like LOS, active state of the target, whether the target is armed, having at least one remaining weapon within range, etc.
I just spent about 30 minutes recreating every possible scenario from this image and tested them a couple hundred times each and it works every time, so I think there must've been something else to this situation that's not apparent. Doesn't seem to be anything wrong there.