Don't turn on the WS4s. Just try to pair it with your Deus controller. Make sure its serial number is still in the pinpointer menu in your remote controllers Option/Pinpointer/settings. You could try removing the serial number and re-pairing it. Whenever I use it with my ORX or Deus I turn on the remote controller first, then turn on the Mi6 an make sure it is paired up, then I turn on the WS or WS4 so that it is slaved to the master remote controller and not acting independently.
I use my Mi6 both paired to my ORX/Deus controllers and unpaired with other detectors. When I want to use it with my ORX or Deus, after using it unpaired, I always have to reset the Mi6 on setting 7 by turning it on, holding down the button for around 5 seconds and then after the melody pressing the button 7 times.