While loop

[jay (support)]

So it seems the underlying condition is the right approach; I'm hopeful that someone may have some insight into what exactly is wrong.

It's very likely Insteon signal issues. I posted a link above to the powerline troubleshooting wiki page that describes how to diagnose those kinds of issues.

Thh while loops are working nicely - in a hybrid mode: I have three devices - starting the first while loop, turns the device on or off; when successful, Indigo triggers the second one, which when on, triggers the 3rd one. No runaway loops.
If there is a runaway condition (which I've seen in other circumstances), how does one stop the loop with this method you suggested?

[jay (support)]

Since you are running it as an embedded script, the process that runs the scripts sets a 10 second limit on the script. If it doesn't finish in that time, then it will kill the script.

That's a good feature, but actually, they are not embedded. I'll move them.