Extreme gain fluctuations

Hello everybody. I am very happy with my denon booth but several months ago I started to experience problems with the gain of channel 3 of my X1800 that makes it impossible to control the sensitivity of the channel since there is a point at which if you turn one millimeter the gain starts to clip. For example, I am mixing with the channel LEDs at -8dB and, if I turn the gain by just one millimeter, the white LEDs light up at +3 dB. I have had the mixer repaired in an official technical service here in Spain in which the channel 3 gain potentiometer has been replaced but, to my surprise, when I get home and start testing the mixer it still has exactly the same failure. In the video (which I recorded after the repair) the gain fluctuations are perfectly appreciated, which is in perfect condition, are perfectly appreciated. I am writing this post to find out if it is a known bug, if it has happened to someone else and if anyone knows a way to fix it. thanks to all.

You should bring the mixer back to the service center.

I am completely sure of that although I find it strange that having changed the knob it still fails.