Hi mate, well I guess that there is something in the ignition system. Specially the ignition switch and kill switches. Some time arcing inside the switch can be a possible cause of this misfire. The loud bang or shake means that there is a complete cut off of the ignition to both the cylinder not just one. if one cylinder is misfiring still the engine will run, but if both stop firing for a fraction of a second, then the result will be a big shake or bang.