6 blow and draw
Ok I been Playing Harmonica for a month now. I have a key of C older Special 20 that I bought new years ago and never had the time to learn. I learn Real real fast. I play 8 different instruments. Any way now I have the time. I Bought A special 20 progresive in the key of A and it was out of key so I sent it back. Then I tried a Harpmaster and it was hard to get any volume out so I sent it back. Then I bought 2 Crossovers. One was out of tune the other the 6 draw was hard to get anything out of, and when I did it sounds like a goose. Next I thought I would try a sydel or a lee oskar. My question is, you think its me? My wife thinks its strange sending all theses harmonicas back. My old special 20 sounds great as does my older Marine band in C. Maybe its the key of A and D giving me trouble? Not sure.
Having this many different harmonicas malfunction is highly unlikely. It's possible but i think you'd be well advised to look at how you're getting notes to sound.
How you move breath through your lips, oral cavity (controlled by the tongue) and throat can all create the effects you describe. And yes, sometimes certain keys of harmonica can be harder to control than others.
Try moving breath gently from deep in your lungs. Sucking or pushing air with your mouth will make reeds malfunction.
The idea is to let your breath flow silently and without any drag in the flow from your lips, tongue, and throat.
Try playing a note, and continue breathing while you take the harmonica out of your mouth. Hear anything? If you do, that's a problem. unobstructed air movement is silent.
Experiment and observe along the lines I suggest. You may see an improvement.