Initially I thought the broken electrode could have been caused by water in the gas but then you showed us the pic of the lower transfer broken off. Looks more like the lower transfer broke off, got blended up by the crank and injested through the transfers and broke the electrode off during compression.
I've had water in my gas on a snowmobile before that was causing it to ping hard and it broke the electrode off the plug. I got lucky and it was ejected through the exhaust with no damage to the top end. Almost burnt a hole in the piston.