@mikeysweet 

If the slave units are going red then it is no longer getting a connection or getting an IP address. You will need to move the Deco units closer to the main one. A devices directional distance does not really equate to how the wireless signal will behave due to reaction from different barriers.

@Tony 

I have the same problem. I just got my Deco X60 yesterday. After finishing installation, the slave deco units keeps changing from solid green to blinking red every 30-40 secs. I have the main deco connected directly on to the modem, and uses a tp link 5 port unmanaged switch going to the other two deco unit nodes. Of the the two nodes, one shows a solid green light, and the other keeps blinking red. 

I've rebooted the system, and even reinstalled from scratch but same problem persist. 

There was an issue with the X60 and the satellite units blinking when trying to be added. To make sure the issues are not related to that, make sure the X60 is running the latest firmware. For the v1 that would be 1.2.6, and for the v2, it should be 1.0.5.

@Tony I have the same issue. The firmware was updated successfully, but the issue still exists. 

@scorching  I was able to identify the issue for my Deco X60. It turned out that the firewall appliance I also had on my network was causing the issue. I systematically went one by one removing wired devices until the blinking stopped. It was my Firewalla firewall appliance. Even though I went in and told it not to monitor the Decos, it still caused some conflict with them. I spent another 2 weeks trying to troubleshoot why the Firewalla was causing the issue, but could never find the reason why. 

Here's what I did to find the culprit:

Factory reset your Decos

Only have your internet device powered and plugged into the Deco

Setup a new wifi under a new name so that non of your devices can connect to it just yet. 

See if it starts to blink. 

If it does, then your internet device may be at fault.

If not, then start to plug in one by one each wired device. 

Wait a few minutes (about 10min) and monitor the lights. If they stay green, continue the process. Once it starts blinking, then the last item you plugged in is at fault. 

Good luck. 

@mikeysweet Thank you so much for your suggestions. I do not have many wired devices, only a few. And those wired ones do not seem to cause the issue. It turned out the problem was due to the Circle, which monitors all devices in the house. After changing the two routers to unmanaged in Circle, issue was solved. 

@scorching I Also have this issue. But the problem was that I have devices in my network with fixed IP addresses which were still being given out by the DHCP server. Ones I had these reserved, the problem is solved.