Headphone issue on BMPCC 6K pro

I've just bought a new BMPCC 6K Pro. Firmware 8.1. Just testing the audio. Using two 416 mics with phantom power switched on, the audio is feeding individually into ch1 and ch2 and both mic levels look fine on the meters. However, I can only hear audio from Ch1 on my Sony MDR 7506 headphones plugged into the headphone socket. I've swapped the mics around and changed audio leads. All works fine. I just can't get audio from channel 2 into my headphones. I've now tried three different pairs. Very frustrating.

Does anyone know of a reason for this problem and how do I fix it?

Many thanks.

The problem is now solved. Thank you