this happened to me 2 years ago while riding out in the woods 100 miles from home
never happened before, or since
fucking castle nut sheared the cotter pin and back right wheel/tire/hub came off, i was in 2nd gear going through some puddles at the time luckily, just 5 mins prior we were flying down a dirt road in 6th
i had another castle nut and pin back at truck, but the fuckin axle sheared the valve stem in half flush with the wheel. no spare wheels/tires with me, day over. lesson learned, put the flat tire back on with the new nut, and rode 5+ miles back to the truck like that
realized afterwards, when putting it back together, that without an extension on my socket, i can get it tight, but then with a pipe on the handle, i can get it just tight enough for the next hole on the castle nut to line up with the hole in the axle , so basically it felt tight without an extension, but wasnt tight enough, could have been disastrous, ever since then i still worry about it and check every castle nut and cotter pin, and all the suspension bolts before riding