See if you can find the "velocity curve" setting on the keyboard. This adjusts the actual volume of the sound in relation to how hard you hit the keys. Some curves are steep (it jumps a lot with little velocity change) and some are smooth.

Steep setttings are good to have if you want to make a significant change. For example if you want to control which sounds comes out determined by how hard you hit the key; a different sample or even a different patch can be triggered by velocity..

Some patches (like piano) may need a smoother setting. This may be the cause of the issue you describe.

I do not work here, but the benefits are still awesome
Make your sound your own!