Naw, I don't buy it. That's like having all four wheel bearings seize up on you car at the same time while it's sitting in the garage. The motors would have stalled and caused 7 kinds of racket. That unit has no overload protection on the motors so it would not have "detected" the stuck bearings. Something else you did got the motors moving again. The chances of having all the bearings fail at the same time is about as high as winning the power ball lottery twice.
It sounds like the motors were not powered up. They will "lock" as soon as they are under power. Servos will hum and steppers will start to warm up. MACH does not know if the motors are not powered up or not turning.
TOM caudle
www.candCNC.com