DJM-750Mk2 only one Headphone working

I recently bought a DJM-750Mk2 (less than 1 month ago) and now my left headphone suddenly stopped working today. The issue is for every channel and also on the master. The master output is stereo like it should be. I am familiar with the mono split function and it is set to stereo. I also checked if the headphones still work and tried it with different ones. This happens on both headphone jacks.

Now I just wanted to know if there is some kind of balance setting I didn't find in the manual or something else I don't know that lead to my problem. I want to make sure I don't return the DJM when it's just me doing something wrong. If it actually is a hardware error I have to return it.