DDJ-RB Problem

It has happened to me that with my first DDJ-RB the volume fader of both has been damaged, it is unstable and does not reach the top, however when I raise the "FILTER" knob to the maximum, this volume is compensated, it is as if there were something between these two elements.

After some time, I got another new DDJ-RB, and the exact same thing happened to it, is this a problem with the model? It's a shame because it's a very comfortable and useful version to work with.