Hyperdeck Studio 12G stops recording for no reason

Our Hyperdeck Studio 12G stops recording after about 15 minutes for no reason. It happens when recording live camera shots and also just when recording video bumpers in a loop. I have reformatted the disk (using SanDisk brand), power-cycled the device, and tried a different CODEC and it still happens. It was working 2 weeks ago and now is having problems. Does anyone know how to fix this?
Thank you
Mike
Thank you
Mike