When a spoke breaks, it places tremendous stress on the spokes next to it. In many cases, this is not a problem but in most cases on cargo bikes or heavily loaded bikes the two adjacent spokes to the broken one will be seriously weakened. On my bike, it is always the drive side spokes that break and I replace them in sets of 3. It could also be a problem with the wheel build causing strain on the spokes, but I couldn't tell without looking at the wheel and even then, i might not see a problem.Vik is correct in stating that a symmetrical wheel will be much stronger. Also, if it is a machine-built wheel, it should at least be re-tensioned and possibly rebuilt by someone who knows how to build wheels.