@David-TP 

I have now successfully connected a Deco to the VX800V via cable.
Unfortunately, I have the problem that although the other two Deco are added during setup, they disappear from the network after a short time and can only be added again after a factory reset.
Unfortunately, it then repeats itself.
Are there possibly certain WLAN settings on the VX800V that cause this?
Possibly with settings that the Deco cannot cope with?
I have written the same question to support and am waiting for a reply.

Addendum, one day later.

The other two Deco are now connected to the network, but unfortunately this is only possible via a cable connection, which is not the purpose.
As soon as I remove the cable, the Deco loses the connection and no wifi connection is established.
Furthermore, the entire EasyMesh network behaves strangely.
Despite the cable connection, it says that the connection is weak.
The Decos and the VX800V are spread over 3 floors.
None of my wifi devices connect to the Decos, they all only connect to the VX800V.
The Aginet app says there is a connection, the Deco app shows me errors.
I have added pictures.

  @David-TP merhaba deco x50 cihazımda 1.ana routerde ipv6 çalışıyor ama 2.ci deco x50 de kablolu bağlantıda çalışırken kablosuz bağlantıda çalışmıyor.Bunun çözümü nedir?

Deco X50 _V1_1.6.7 Optimized the Client Network Stability nerden indirebilirim.Denemek istiyorum.

Hello, on my deco x50 device, ipv6 works on the first main router, but on the second deco x50 it works on a wired connection but not on a wireless connection. What is the solution to this?

Where can I download Deco X50 _V1_1.6.7 Optimized the Client Network Stability? I want to try it.

  @mariocaz i was on 1.5.5 

  @JanRekenaar 

What was your last version ?

@David-TP I bit the bullet and installed 1.6.7 last thursday. I tested and stresstested the app and my 4 Deco X50 v1 (EU)  the last 4 days. 
 

I don't wanna jinx it but.. no crashes. No red lights. No incorrect clients. Everything looks stable and reliable. 
 

I hope this stays this way but this looks promising. 

  @David-TP 

Yesterday nite I did the firmware upgrade to the version that was available at my APP and looks like everything is working fine at the moment, if all still good, do you recommend me to upgrade to the 1.6.7 version ?, thanks, hope you answer me.