My guess is you badly misplaced the humidifier on the leaky night.
You arm hand and fingers probably remember the movement you used for the A10, and (assumption) you don't have the advantage of hearing a the click when you insert the humidifier in the AS11.
Try to go about it very slowly and consciously, searching for whatever it is that will give you feedback about the correct placement.
Use the "test maskfit". And do this whole learning session when you're wide awake, i.e. not just before you're going to sleep.