Hi, It's possible you are working too hard with the clearing, which is easy to do since we all want to get airway clearance over ASAP! Huff coughing is quite a gentle maneuver. Perhaps review your technique -- here's a child demonstrating the huff cough. I often go back to it as a reminder to be more gentle.

Also, what are you doing prior to beginning airway clearance? It's fairly standard practice to inhale a bronchial dilator such as albuterol followed by hypertonic saline. Presently, I use 2 vials of 7% hypertonic saline. While inhaling the saline I stop every now and then to use the huff cough to clear. Years ago I used the acapella and then moved on the aerobika then onto the AD app. After a lot of trial and error I found these devices less effective than the huff cough on its own. It's really what works for you. Hope this is helpful!

PS - I also take 1200mg of mucinex 1-2 per/day with a full glass of water.