Push notifications to iOS require WiFi link when Ethernet used

There appears to be a bug in iOS (10.3.1) with push notifications and Ethernet. We use the Apple Lightning to USB 3 Camera Adapter and a USB Ethernet adapter to provide network to devices in the field. During a troublesome deployment we discovered that the Apple Push Notification Service (APNS) does not establish a connection if the WiFi radio is off or not joined to a known network. That WiFi network does not need to have valid internet, or even DHCP available, the device will choose a self assigned IP and then the APNS connection will use the Ethernet adapter.

I imagine this has something to do with how APNS behaves when both Cellular and WiFi are available. I'm curious if Apple TV has a similar bug, I imagine not, given the fact the Ethernet is built in and likely a more common scenario. Although a seldom used feature, the Lightning to USB to Ethernet configuration was feature in a past keynote (https://sixcolors.com/post/2016/03/apples-lightning-to-usb-3-adapter-bri...).

MDM commands are triggered by APNS messages which means MDM is not functional in an Ethernet only environment.

It was a tricky one to discover, requiring packet captures, and other network analysis to isolate, I hope this helps someone else in the future.

Radar:
http://www.openradar.me/31494325