I had 2 devices connected to my M5 Deco using both the WAN/LAN ports. M5 is set up at a Router.

1. ONT fibre

2. TP-LINK AC1300 Powerline

After a power outage, the DECO M5 is unable to find out which devices (1 or 2) is the ONT Fibre to grab the WAN address. 

LED remains RED.

Solution:

1. Remove the TP-LINK powerline first. Only the ONT and the M5 to switch on first. Plug the network cable back in the powerline.

2. Use another router with a DEDICATED WAN port and connect the M5 as an AP/repeater.

3. 

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I hope TP-Link can come out with a firmware that fixes this issue so i can have 1 less device running at home.