crap design, IMO
bad boy knows it too.
How many hundred have I fixed? Hmm...I forget.
it's not always but often related to mowing with the deck riding the ground, e.g., mowing too low, rough terrain, getting up against fences/curbs/sidewalks, sometimes worn out/unbalance blades cause vibration which then contributes as well
often people blame the weld and even properly welded, there is always going to be a heat affected zone, where the material is weakened a little near the weld. This is even apparent on the factory setup. They do what they can within the constraints of manufacturing to minimize the HAZ but they can't totally eliminate it short of heat treatment-which adds significant $$$ to the cost of the mower, which then makes it more expensive than the Kubota or Deere counterparts, of which they were competing with.