Have you successfully configured the ADC on this chip model before? I've been through the ADC docs for the PIC32MX/MZ many times and they're quite dense. It would be very easy to miss some required configuration bits.

In my experience, it's never a problem with the hardware itself, but you never know. I spent 3 weeks last summer debugging a problem with the MRF24WG0MA, and was almost convinced the chip was defective, until I realized that Harmony configured a few things incorrectly (the interrupt polarity being one of them). But yeah, for a show stopper issue that I'm not making any progress with, I would just get in contact with the manufacturer.