Without knowing what broke it is hard to say. It's unlikely they are the rare ti spindles. Unless you are a clyde with gobs of power.. it's seems very strange to have broken 2. If you assume the spindle is broken I wonder if it is failed bearings? You would know if the spindle was broken because the arms would be all floppy, so if you are assuming.... well then the spindle isn't broken.

Who did the last service on the BB? were both cups tight? many factors here. These are the best cup and ball type of BB you can find, they rarely fail.

This sounds like service error.