If the pedal assist power is intermittent, check if the PAS magnet disk is wonky, like the one below! Please ensure that the disk is straight and that the sensor it pointing at the magnets on the disk.
This should fix it! If it doesn't, look here: https://swytchbike.zendesk.com/hc/en-gb/articles/360016217494-My-motor-is-jerky-or-not-working-at-all-