I had a power outage and my mesh network was not working.  Had a solid red light on the main unit (the one connected to the modem) and flashing red on the other units.

I followed instructions in this thread:

https://community.tp-link.com/en/home/forum/topic/220354

Did not work.

Tried a factory reset (button on bottom of unit).

When setting up network in the app I ran into a problem.  The app keeps telling me that the device cannot detect the ethernet type and that I need to connect the ethernet cable.

Followed the advice in this thread:

https://community.tp-link.com/en/home/forum/topic/614200

Did not work.

I tried a different unit (did a factory reset and started the process over again)

I tried a different ethernet cable.

I treid different ports on the decos and the router.

Did not work.