I have an Argon as gateway to wifi and successfully connected a couple of Xenon devices. I have since done a reset of one of the Xenon devices (Hold mode button down until led is flashing blue). Using the app to reconnect, it will no longer go all the way through the mesh connection process and stops with “Adding Xenon to the mesh network” in bold.
Devices all at 0.8.0-rc25.
Phone used to activate: Moto C plus; android 7.0
Particle App: 2.3.7