Bluetooth dropping out during setup

Successfully setup Argon and 2 Xenon a couple of weeks ago. No problems.

Today I thought I would try the Particle Ethernet Featherwing with the Argon. Of course needed to setup another network but no problem. Added a Xenon, no issues but adding second Xenon I get “Error - The Bluetooth connection was dropped unexpectedly. Please restart the setup again”. I duly did many times. Even got as far as putting the network password in on one occasion but before it connected Bluetooth dropped out again.
Distance between devices is only a couple of inches.
Any ideas?

Done a bit more sleuthing.

Using IOS 12.1.2 - Latest device firmware.

Setup Argon gateway on a new network on WIFI (not ethernet featherwing).

The problem is not device specific. Swapped the Xenons and it is always the second device on the network that has the problem.

Tried disconnecting the first device while setting up the second - no difference, still Bluetooth disconnecting.

There is no specific point in the setup procedure when the Bluetooth drops out, can be after pairing or during password entry or anything in-between.

More (probably the last) info. Plugged second Xenon into Ethernet Featherwing and wow it connected to network. BUT
whilst first Xenon was breathing it was not showing on the Particle APP. Pressed reset and - flashing blue . Not part of network so - conclusion is - only one Xenon allowed on network (at least for me).

Anybody out there got any thoughts???

Final, final edit. ‘Forgot’ Argon and Xenons through device inspector. Started again with Argon as gateway and sequentially added the Xenons - now all talking to each other.