DJM900NXS headphone cue issue

This has happened three times at venues and I can't recreate the issue at home - the headphone cue for the 2nd channel doesn't work when the headphones are in stereo mode, only works with mono. The button lights up but the sound doesn't come through when it's set to stereo.

The first time this happened, an hour or so into playing it started working again, but the second time it stayed like this the whole time. Last night it started happening halfway through the night. However, when I set it up at home today, everything worked perfectly.

Can anyone provide insight as to what they think is going on here or what I should do? Another audio bud suspected power supply issues, which would make sense. Turnaround to get it fixed at the corporate repair spot (which they can only do if they can recreate the issue) is like 2 months so I'd love to hear your advice before I surrender it. I'd almost prefer it not work at all rather than only sometimes lol it's so annoying. Thanks in advance!