Maybe this is also of importance that the CC85xx slave module (your hardware) is placed very close (<10 cm) to a digital amp and PWM-driven FET-based power volume control. The output PWM power signal at 176,4 kHz is not currently well filtered so high-frequency Fourier step signal products can be in the air around - can it affect the range siginificantly ? If so what can I do to best test this hypothesis - place e,g, a metal sheet between the two modules ?
Regards, Pawel