@TP-Link 

Same Problem here with 3x PX50, 1x X50-Outdoor and 1x X50. After adding the X50 via LAN it worked awesome for ONE DAY and in the evening, there's not even one LAN connection made anymore and everything tries to connect via WiFi. This is bonkers.

Firmwares:

PX50's: 1.2.1

X50-Outdoor: 1.2.4

X50: 1.3.1

It is such a disgrace. The 3x PX50 worked together perfectly, and we felt so lucky to finally have a great powerline solution. The added X50 broke everything.

Currently, we still have 1 week left on Amazon to return everything… I'm pretty sure, that has to be our “WORKAROUND” to this mess.

Same issue here with Deco E4 v1.

Went mad after a few power outages caused chaos with home network.

After a complete reset, I had things up and running for a sustained period only to find devices would randomly drop connection or be unable to connect at all. I'd have a device with wired connection working just fine but wireless device would not be able to connect and wired connection to main unit broke everything. 

I was forced to switch from router mode to AP mode for my own sanity and have now had a constant network for 24 hours. BUT if I dare to connect a device as wired to the main unit, internet connection is dropped for all devices. 
 

Then I came across this topic and learned that some design decision is behind this! 

Deco E4 v1 hasn't seen any firmware updates since 2021 - is there something planned?

  @TP-Link 

I also have same issue with my deco x20

My CCTV decoder always disconnect 
Before I use deco x20 there no issue my cctv disconnect 

  @ah1stb 

I finally got my network stable. See if this works for you. Set up your main DECO and WAN and leave it as wireless BEFORE you add any LAN nodes. Add your LAN back slowly until your whole LAN is back online. Then add the deco's back to the LAN one at a time by plugging them into the LAN until all are back online. 
 

Alternately, you can try to add your main deco and LAN, before adding any satellite decos.

What was happening to me was I tried to add the satellites back to the LAN before the network was stable and completely reattached. I had unplugged my LAN nodes and tried to add them back in a sequence. The wireless nodes were connected to the WAN and portions of the LAN simultaneously and they were competing with the main deco in supplying internet to the LAN. Once the main deco saw the competing signal, it shut down the LAN ports.

hope this works

  @TP-Link I am having the same issue.  My DECO X75's are brand new.  Everything was working flawlessly, all of a sudden my whole wired LAN network dropped.  No WAN access.  Tomorrow I will reconfigure to use my DECO in my upstairs office to use one of the ports on the back of the AP to be WAN and plug my LAN back in.  Confirmed I cannot have more than 1 Ethernet port plugged in now.  FOR NO APPARENT REASON.  I can only have my WAN plugged in.  I would like a new unit shipped to my house to replace this product as it is less than a month old.  I cannot use all the ethernet ports anymore.  Only 1 dedicated to the WAN.  Do you have an advanced utility I can use to change the port to be LAN DHCP only versus this auto sensing tech?  I have extensive network knowledge and there is no reason that the user interface has no real Advanced user options.  I settled for these devices for simplicity as my wife was always complaining about it, but at this rate I will never purchase TP Link DECO products again.

I am short of setting up a switch and packet capture to analyze why this is happening, especially on a device which was working.  For now I am on WiFi, but I need my LAN wired connection back for my internal network setup.  I can't even connect a single laptop to the DECO x75 unit that is getting my WAN connection without it dropping internet and going RED.

Please assist.

  @TP-Link  2 days I've spent on this, switching out cables, switches, deleting and recreating networks. I can plug my pc into port 2 directly and get internet access. Once I plug the switch in, nothing. How can I have internet directly through the 2nd port, but my switches and the other 69 wired items can't have internet when plugged in? Please help. If I buy new and this isn't fixed, It won't be TP-Link. And I'm all in: 4 M5's and 1 x50-outdoor + several switches. Please help fix this.

For X50 it is still broken. Don't optimize it just f***g fix it. If you are too stupid pay someone to fix it. How many more years you need? It's unbelievable. Home automation, including heating, gets down because you hire low IQ developers.

Just give us option to set WAN port manually.

  @David-TP This beta firmware did not work, my port 1 is still non-functional.