Sorry for the delay. Looking at your snap.yaml, you have this:
It seems you may not have considered my previous comment and the new thinking around the content interface. In the snap’s current form, -1.
Assuming you built mir-kiosk on 16.04, if you update the snap to use this (modeled after the gnome-3-26-1604 snap):
(or something similarly clear that it was built using 16.04 environment), then it would ok to grant auto-connection. Please see the links in my previous response if you have questions as to why this is required.