Pioneer 750MK2 Problem Mixing Button Headphones

My Pioneer 750 MK2 barely a few months old,when i press for example the master cue button when i turn the mix button on the headphones to the cue position i still hear the master and if for example i select the cue button of channel 1 or any channel when i turn the mix button on the headphones to the master position i still hear the cue of the selected channel, it's like when i turn the mixing button i always hear the master wherever i turn it, the curious thing is that when i check other buttons when i turn the mic button low i get the volume of the headphones up and down.

The surprising thing is that it always works well and when I turn it off and turn it on another day there are times when it doesn't work well and this problem occurs with the mixing button and other times I turn it on and it works well.... what I find strange is that there are times when I turn the LOW button on the Mic and it modifies the volume of the headphones.... as I say it doesn't always happen but since a few days ago it happens randomly.

What solution do you recommend? it is very strange, previously I had pioneer 500/700 and these new Pioneer with so much digital software does not give me the same fiability and I thought it would be a better table but if in only 4 months it already has this error, it is not normal.

I never had to repair any of the previous Pioneers I owned, they were reliable and tough mixers.

Best Regards