sounds to me like he needs to check a couple of things before I/we blame the controller.
1st pull the battery out and clean all the corrosion from under the battery, a lot of wif [Weird Intermittent failures] are caused by signals through the frame and battery corrosion. replace ANY power cable that has been laying in the corrosion and has ANY damage or change to the insulation.
2nd, talk a good eyeball to every one of the traction motor brushes, make sure they are not stuck in the holder and are free to move and not worn out and the brush springs are good.
THEN if you still have wifs, start to consider the controller.
just my.02USD