The cfg[MAC}.xml contains invalid data. Phones will not provision. If you manually change the phone type to 2130 instead, they will provision. This occurs regardless of phone firmware. Grandstream has confirmed this to be an XML issue via packet capture.
We can duplicate this issue on 3 different Yeastar devices running the latest firmware with more than a dozen GXP-2160 phones.
Other grandstream models work fine on the same devices.