Update:
I updated the firmware on my Argon & Xenons via USB and the particle cli instructions.
After a false start where I tried to bring up a xenon without a mesh network within range (so I created a mesh network by claiming and configuring the argon first) - I was able to add 2 xenons to the mesh network - all using my LG G5 phone.
I exited the setup process at this point and tested these parts using the app to twiddle D7 on all 3 devices.
So far so good.
I go back to add more xenons to the mesh and now after I select the mesh network, I get this screen instead of the one where it says “joining the mesh network” etc etc:
The xenon is already flashing blue at this point, and continuing to scan the 2D barcode doesn’t help at all.
I’m a little baffled what backwater of the process that I’ve got stuck in, it seems like when I claimed and configured the first two xenons, I was in a mode where the app had maybe cached some info, and that got lost when I exited to toggle bits using tinker.
Maybe this is intended behavior - I’m not sure why the flow is different from the first two xenons I configured, but I’m unclear how to proceed.