Are you powering everything at the same time, or is it possible that the motor connections might e.g. have pullups that are powered before the Edison? I ask because I had a problem once with an STM32 based system where I was powering an external device before I powered the MCU. The external device was feeding a trickle of power into the IO of the STM32 that was just enough to make it boot into an unusual state.
Was the previous suggestion helpful. Let us know if you still have questions.