I think from my own experience and what I’ve heard that it’s not uncommon — with Yamaha pianicas –to have trouble with a note or a few notes not playing or requiring special attention. I have found that working on the problem key or keys seems to “loosen the up” though I’m not sure that’s the right description. I’m talking about blowing and sucking on those notes. Over time the situation seems to resolve itself. Yamahas are among the best melodicas, in my opinion. Sometimes they’re sticky after not being played for a while (a week or two) and need a little warming up with scales or arpeggios before being played. Sometimes I blow moderately hard and just run my finger down the white keys and down the black keys a few times. I think as you play the P-37D over time there will be less of a problem and it will be more satisfying than most other melodicas. This is a very good instrument.