I believe I know what happened after talking with their tech.
This could not have happened from over torquing the main drive nut. The marks on the nut were from his impact on the low setting (45 ft-lbs) and he torqued it by hand. Over torquing this bolt would put pressure on the bearing and it's not possible for it to move the crankshaft since it pinches the side of the case.
What we think happened was that the key in the balancer sheered off over time. This bike saw a LOT of freeway. At high speed the balancer was making contact with the crankshaft. The crankshaft has a small amount of play side to side from the factory, this is that gap we see in the bearing seat. The crank likely saw a lot of vibrations and this caused the main drive pin to come loose causing the balancer to spin freely and leave the engine.
So I think the weakness is that balancer key, this can cause your balancer to loose timing and hit the crankshaft. Over time this can cause the crank to shift side to side and the main drive pin to come loose.
It blew when coming off the freeway. Before that it made a sound similar to a misfire or exhaust leak, this was likely the balancer hitting the crankshaft.
See the failing balancer key here.
https://i.imgur.com/VEBUgRo.jpghttps://i.imgur.com/F7ldFCB.jpgIf you use this bike for a lot of freeway riding this could be a major failure point to watch out for. The balancer has springs to dampen the rotational force so although it has a 1/2 inch gap when not moving when running at a high speed this gap will shrink and if the pin starts sheering off it gets even smaller and it can hit the crankshaft.
Hopefully this makes sense and provides some closure.