A clogged filter will cause this. I know you said it was clean but they can be clogged and still look clean on the outside. Try washing it under running water the let it completely dry overnight.
it can be due to a battery of the cleaner. Make sure that the power cable is properly plug to the power and seated properly from the unit while charging. If you find that the battery isn't charging at all, you may need to replace the battery. Second is to check the MAX button of your cleaner. If the button lights up and flashes when your Dyson keeps on pulsating, press and hold the power button and depress the MAX button to turn off the function. You may need to do it for a few times to get the hang of it.