JVC KD-AVX44 no sound in normal mode

Question

I've just installed this unit and there is no sound in normal mode but as I switch on the DUAL mode the sound comes out fine, I am using ISO connectors and 2nd audio out is not in use also there's an external amp connected to the woofer out to power the sub-woofer. the main issue is most of the features like USB and bluetooth dont work in DUAL mode so there is no sound when I connect my phone via bluetooth or USB drive.
Any help is much appreciated.