sudden volume increase (RPI3)

I noticed that my samplerbox sometimes plays a note a bit louder than the other one. It seems completely random (can be any note, sometimes almost never happens and can happen every 6-7 notes on the next day).
It is not a huge difference, but enough to notice and to be a problem if I were to use my samplebox in a live setting.

Has anyone noticed the same problem?

I installed the samplerbox on a raspberry pi 3 if that makes a difference.

Try another controller, this is a common glitch on many controllers, especially when they get old, the velocity is misinterpreted as full.