When playing a chromatic harmonica, it may sound fine at first, but after playing for some time, the beginning of notes may start to feel slightly blocked, and very gentle breath may no longer produce a sound.
At such times, if you blow a little harder, the note may suddenly burst out with a “pop” sound.

This is caused by the harmonica's internal valves (windsavers) and is not a malfunction.

To prevent this phenomenon, it is important not to let the harmonica get too cold. Before playing, keep it warm by carrying it in your pocket or holding it in your hands. This helps prevent moisture from condensing on the reed plates.