OK, update to my issue at least. The Kestrel will NOT accept any range information inside of 100 yards from the Fire4000.
Going off what you had said skyewalker, I tried connecting to the BOSS app just to see what it would do. It connected just as expected to BOSS. While still in the BOSS app, I turned on the Kestrel and had the same experience as you were asking about. The Kestrel would not connect to the Fire4000. Shut off the BOSS app and restarted the Kestrel, and it connected up as expected.
Here is where it gets interesting, when I tried ranging again, the Kestrel actually gave an error, "Received invalid target data" which it had never said before. So communication was obviously now occurring! Armed with this new information, I went outside with the Fire4000 and the Kestrel. Anything from 5 yards out to 95ish and the Kestrel would always say "Received invalid target data"
Once I found something beyond 100 yards to range, in this case 167 yards, it sent the data to the Kestrel, the Kestrel updated the yardage and I had DOPE on the Fire4000! Tried again on something closer, 26 yards, and once more the Kestrel showed "Received invalid target data"
I need to pull out my VectorX and TerrapinX and get the Kestrel paired to either of them and see if the same "inside of 100 yards" causes the Kestrel to throw an error.
For now, I am happy with this knowledge. Not like I'll be doing many inside of 100 yard shots with a 6.5 CM or 300PRC. But rimfire is another matter. But really, that isn't that big of a use case for me.