MOSFET Driver Stress
I would suggest you to monitor the xHI and xLO signals getting inside A4935, and also the respective Gate output from the A4935, using oscilloscope. Sometimes, due to switching of large current, there is a lot of EMI noise that penetrates in these small signals. And false trigger your MOSFET. Resulting in occasional Short-circuit condition.

I would also suggest to add 10K register between every MOSFET's Gate and Source.