Do you have an enclosure? It could potentially be a faulty door closed sensor. If the sensor isnt triggered (i.e. door is open) it reduces the laser power so that nothing can be cut. If the sensor is faulty and intermittently showing as open then it could cause this?
If you want to test this, you can deactivate the door open sensor. I think this can be found either on the touchscreen menu or in Luban settings.