I am using an iPhone 6s into an H/K Business CD connected as follows:
Phone lightning connector to USB to 12V lighter jack
Phone 1/8" plug to Aux in

With increasing frequency, the Aux input is unstable. It drops out and switches over to the radio seemingly at random. There is no particular sense of vibration or road bump associated with this. The iPhone has to be completely disconnected and reconnected before the Aux input becomes selectable and usable again.

I have swapped out iPhones, cables, the 12V USB adapter: nothing works. Caig Gold applied to the contact points may help (hard to tell) but not for long.

I installed the Aux input adapter in February. I know I did it correctly.

Suggestions? I'm going crazy here....