@MeOverHere Sopme further checking: The Deco app shows no device has easymesh active and I am not able to change to another X50 as Main Deco either.

  @MeOverHere firmware 1.8.0 does not support easymesh.

  @bobvana I know that neither the X50 nor the BE25 support easymesh and still I get a message that I need to disable easymesh as it is not supported and my WiFi backhaul on both X50 and BE25 is broken. I have never used easymesh before. BTW, my router is a Ubiquiti UCG-Fiber so that should not cause any issues. 

  @David-TP 

This is what I get when I try to change the Main Deco from an X50 to a BE25. I have upload the Deco APP Log.

  @David-TP It works again, but I had to reset all 6 Deco's I have and rebuild the network from scratch. Even then, "Replace Main Deco" did not work, but set new "Main Deco" worked after a new device was added. If you would set a custom name while adding a Deco unit, it would default the name to name you get if you skipped the step. A custom name could not be set unless one of the fixed default names was selected first. The main screen of the APP looks normal again. Before the rebuild it did not show the Main Deco and you had to plress on "everything looks good" to get a list of Decos.

I have a similar problem.

Main BE25 deco, then another BE25, three XE75, and two X50.

Yesterday, both X50 were offline (flashing red light).

Unable to reconnect.

After resetting and reconfiguring them, they started working again.
After rebooting them, same problem, and no way to reconnect via WiFi to the other decos.
Reset again, reconfigured, and they worked again.
Rebooted again, still offline.

The only way to see them online after a reboot is to connect them via cable.

I also noticed that after each reboot, the main and guest WiFi networks disappear, while only the IoT network remains visible.

It seems that after a reboot, the WiFi stops working, so they can't connect to the other decos via WiFi, but only via cable.

The strange thing is that this issue started two days ago, and the problem occurs even when I add other X50 I had as a spare to my network.

In short, the X50s work perfectly until the first reboot, after which they need to be reset.

Previously (2 days ago and before) , they always worked, and a reboot was scheduled every morning without any problems.

I even tried completely erasing my network and rebuilding it from scratch... Same problem, and always and only with the X50s (both hardware version 1 and version 1.2).

  @David-TP Based on the post by Mauriga, i did a reboot of my Deco system and I get exactly the same: the wify backhaul no longer works after a reboot. I unplugged ethernet from one X50 before reboot and the Wifi Backhaul took over. Then I did a reboot and repeated the experiment. Initially, it was green for a short while and the Deco App showed it was linked through the 2.4GHz/5Ghz link to my main Deco. But then the led went red and the link to the deco was list. Plugged ethernet back in, it works again. 

 @Mauroriga