I have been using 4 Deco X60s for a few months now without any issues but as of yesterday they all suddenly show red LEDs and when I check the Deco app on my iPhone it says that all my Decos are offline. However, using a WiFi-only tablet, I am able to connect to the internet using my Deco network just fine, so they are connected to the internet but signal that they are not ...

I have restarted the Decos both from the app as well as manually/unplugging them, but once they're back up they show red LEDs and I have the same error message in the app.

Although the Deco app did not find any new firmware, the TP Link website did have a new version so I downloaded and installed it using the PC. Now all my Decos are running on Firmware 1.0.11 but the issue is still there.

Any idea what the root cause could be and what to do about it?

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UPDATE

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Turns out that my router had some issues with the DNS (but everything was working fine nonetheless). Once I had rebooted the router, the LEDs turned green. Problem solved :)