if your composer drum track already has notes recorded, (in step edit mode) you have to press the okay button ( bottom of screen), after you've added/edited any of the notes, or else it just reverts back to original note.
ie you press "crash" drum note then press okay icon.
Hopefully this may work for you.
Korg PA4x, Korg PA3X, PSR S950, Band in a Box 2018
V Arranger/Ketron SD2