Happy Thanksgiving! And, thanks for your help! I went ahead and performed the factory reset and flashed tinker to my Xenon. After that, I was able to flash blue for further config.
It turns out, the rapid flashing green was resulting from “something gone wrong” (more below) with my mesh network. My Xenon was dropped from the mesh network and I could not add it back in. So, I needed to remove all devices from current mesh network (just one left, my Argon) and create a new mesh network. Then, add my Argon and Xenon via CLI (did not have success doing this thru the app). All this I accomplished after reading the topic: Remove mesh network
More about “something gone wrong”. I had upgraded to the new Mac OS Catalina where I changed from bash: to zsh: then back again, now staying with bash:. I think this flip/flop caused issues with Visual Studio Code app. And, perhaps, hosed my mesh network, somehow (probably, not so, but I DID make a frustrating mess). Once I was able to settle down VSC app use over the course of a few days I posted for help with something concrete at issue.
In retrospect, when things went bad, I remember the Argon was waiting FOREVER in a waitUntil(Mesh.ready) statement. Both the Xenon and Argon were indicating they could NOT access the mesh network. If I was smart, I would have started investigating right there! Oye!
I am reassured to know I can get these devices back to factory settings. I needed that little push. Thanks, again!