Hi, all. New to the forum, so I apologize if I am not in the right place. Please advise.

I have a Deco mesh with (3) S4 units. Two connect happily (one being the main unit), the third doesn't want to, even when sitting within 4' of the main hub unit. I have rebooted a number of times, pressed reset 2-3 times. It wakes up, then after about 45 seconds starts to flash green/blue, later settling to a steady white/yellow. The app shows it as "offline".

Of inteest: When I ask the app to "check again" to see if it can see the offline device, the device itself does something internallmaking the top light change colors. Still, no connection found.

Idea? Is there a spelled out troubleshooting process that could lead me to a solution?

If part of the advice is to upgrade the firmware, how would I do that for a unit that is "offline"?

Many thanks.