Well, I checked within the app to check the active connections and found out that my mobile was connected through 5Ghz. Unfortunately I can't make screenshots now as our main internet has fallen out and the Deco's should work normally with our internal network but they also have given up due to this I guess, and except for the main they are all blinking blue now, as they want to be set up. Which I can't at the moment. Or I should plug in a lan cable in the main Deco? Tried that but didn't work. And the named wifi on the deco can't also be found anymore. It pops up now with Deco for which I don't have a password, as when I enter the password for my regular wifi-network that one doesn't get accepted. Hopefully when tomorrow-evening the engineer has fixed the problem with the fibre everything comes back up to normal, but I keep my fingers crossed.

Currently almost all my Deco's show up when trying to connect to Wifi as Deco and Deco_something.

During the day until the power got off of the main deco, my regular ssid was shown and I could still connect, but I read in a post from you of 2020 that the deco's need to be connected to the internet to configure. So I guess that during the powercycle of the main Deco finally everything got 'lost'. Then I hope it will come back on nicely. As all my home-automation devices depend on the Deco-network.