I bought my Deco from Costco about I would say 4 to 5 weeks ago. I have been having this issue consistently since I set it up. I originally was running the previous 1.2.1 firmware on the Decos but upgraded to the new version when it came out. I only got one day of uptime before the wired backhaul failed and the internet went down with it. I thought the presence of some D-Link branded switches which were connected to some of the satalite decos were causing the issue since it doesn't support the wired backhaul protocol. However after switching those switches with some unmanaged netgear switches that should support the protocol (I checked via tcpdump) I am still getting the issue.

My ISP is Xfinity and I have my own modem which then connects to the main deco unit. From their I go to a unmanaged netgear switch which run to a patch panel and sends it two other unmanaged netgear switches which have the other decos units connected to them. To eliminate the issue of faulty cables I have tested each cable run with a tester I have and found nothing on that end. Before I had the Decos I was running the first gen Google Wifi mesh routers. I had problems with them as well, but I feel like that might have been attributed to the D-Link switches that were connected before. Since I went back and switched to those with relative stability for now. I prefer the Deco's software control over what the Google has to offer and since I can force device to certain Decos and also prevent other devices from switching at all. I would really like to keep the Decos rather than returning them back to Costco.