Problem could be many things,
such as overheating component, like power-supply, stepper-motor, or on Motherboard.
Could be loose or broken wire somewhere, like at bend on top of extruder motors.
(we had broken wire there once causing intermittent filament feed)
Could be Temp of extruder lowering due to heater circuit problem, or damaged thermocouple-wire.

Those are a few I would check first.