@TP-Link I just encountered this issue recently, please fix!

  @TP-Link Almost a year and still no fix for that issue? Today I had problems with my ISP, and during that outage, I cannot do anything as my whole network was down. Shame on You and You just lost a loyal consumer. Never TP-Link again.

  @TP-Link 

What a dissapointment ... after at least 10 hours of fiddling with cables and settings and waiting for reboots and ... to find out that this is a known issue for so long.

It makes sense to me now, the Deco series was never meant to be operated without a proper router before it, it was meant to replace a wifi network, not the complete LAN function. 

To share what I tried to do: I'm in the Netherlands on fiber (KPN glasvezel) and wanted to get rid of the telco provided modem/router (Experiabox V10A). I did get the main Deco up and running WITH iptv working as well -> WAN in port 3 and IPTV in port 1. What was strange already was that I had to select port 2 if my cable was in port 1 and I had to select port 1 if my cable was in port 2 in order to make the TV work ??? I triend different things to correct that, then figured (guys don't read manuals right ;-) that maybe adding the other Deco's would do something magical (I simply could not think of tplink actually made a design mistake and was still thinking that I did something wrong). Then I tried a zillion other things involving many reboots and cable switching and again and again until I did a google on the topic to find out why the LAN is not working and came here.

All in all a very very bad experience, while I must say, I have been using tp-link  switches both managed and unmanaged for more then a decade with joy and pleasure.

Unfortunately I've decided to return my products since keeping the dreadful PoS of telco provided router and placing the Deco X50s as APs behind it, is not a step forward. It is like fitting a wannabe sports exhaust under a Ford focus 1.0 

With utter dissapointment I'm left to hope that someday TP-Link will either sell this product for what it is (THIS PRODUCT CAN NOT BE USED TO REPLACE YOUR ROUTER WHEN YOU HAVE OTHER WIRED CLIENTS IN YOUR NETWORK CONNECTED TO THE ROUTER BY SWITCHES, IT ONLY WORKS IN AP MODE it should say on the box) or fix this issue properly.

Bye

  @zeusent Two days ago I installed a Deco X80-5G with 3 Deco X50 attached to the X80. The main reason for choosing this system was the fallback 5G function. After the successful installation I recognized that as soon as I deactivate the cable modem, all my via LAN connected devices to the X80 were not reachable anymore and on top had no access to the internet. My WLAN devices were fully functional and the fallback solution to 5G worked. It took me quite a time to figure out the problem, but since I found this forum post, it's pretty clear what's happening. It's autosensing which disables all LAN ports if the cable modem goes down! That's a major bug and renders the idea behind fallback (!) to simply useless. For WLAN it's working, not for LAN!?! What a mess. TP link has to fix this asap. I do think of returning the "powerful" device X80-5G Really mind blowing. 

  @TP-Link spent hours since yesterday trying to fix this, till I found this post. Eventually, I had to press the reset button at the bottom of all of my M5 units, disconnect it from power and start the setup again as if it was a new unit.
Now I have configure all my smart home devices to the new network all over again. What a waste of time.

  @TP-Link I purchased the Deco XE75 2pk this past Saturday and spent hours trying to get it connect correctly.  I have FiOS 1GB internet, cat5e directly from FiOS ONT, no modem in between because the ONT is FiOS' equivalent to a modem.  After being extremely frustrasted, I shipped the XE75's back and reconnected my Amplifi Alien.  I was still baffled as to how in the world a system that so many reviewers tout as "plug and play" and "it's so easy to setup" that I searched and searched as to why this would not work.  Then I came across this thread.  What an absolutely ridiculous oversight on TP-Link to have such a fundamental necessity make them lose customers.  It really bums me out because unless this gets addressed, there is no way I can be a customer.