Mirage Liberty Nasal Pillow Slipping

I've been using the Mirage Liberty for over 3 months. I sleep well for the first two weeks but then one of the nasal pillows starts slipping out during the night waking me up a couple times. A month ago I got a new mouth piece and nasal pillows and I had another two weeks of not waking up. I'm not sure what's going on but does anyone have any suggestions on what I can do to make sure the nasal pillows don't slip? My headgear is pretty tight already. Thanks!