Bolt over torque is the #1 reason that the bolt would break.
This might be because somebody did not torque it properly at a shop, most common. I have seen this in chain drive numerous times.
Or not as common but wrong bolt used for the application. It should be a grade"8" bolt that is torqued to spec with red loc-tite.
Another thing to look for is wear at the hub, if the splines are worn the bolt will never torque properly and the bolt can break.
Sled has 815kms never touched bolt sled bone stock except a can last sled was mod and decided to try a stock sled and not mess with anything. Four trips out two trips to shop, sounds like getting the run around from Polaris about warrenty on my upper structor. Cycle works is doing a great job on keeping me on the snow making tracks. The customer care is really good at cycle works just need the sled to hold together !!
Mine broke at 1200 kms with the TKI belt drive. The significance of this is that I know I torqued in when I installed the drive kit. That eliminates the likelihood that the factory just forgot to tighten it. So far the grade 8 bolts are holding good.