Older issue with alternative workaround.

Similar issue in-
https://community.tp-link.com/us/home/forum/topic/521262

https://community.tp-link.com/us/home/forum/topic/150603 

Likely cause was/is MAC Binding.  "Essentially what is happening is the Modem is still bound to the MAC (media access control) address from the last device that was connected to it."

I switched from Fidium/Fiber are the end of a 12 month intro rate of 35$/month for 50Mb/s $55/month.

Comcast/Xfinity was running a 200Mb/s for $25/month  for 24 months promo - probably to compete with Fidium.

I don't 'like'  Comcast, but one has to  move for $30/month and a lot more speed.

I re-used my (Bestbuy) modem: Docsis motorola 24x8 MB7621 s/n 2110-MB7621-30-5243 

The DECO X60 acted up, couldn't get an WAN IP from this simple-no-router-modem in Deco Dynamic IP setting as 'detected'.

A laptop connected earlier to test the modem worked fine, got an IP as it should, but the DECO wouldn't. 

In desparation I tried both ports; tossed a GB switch between Deco and Modem; switched on  'Unicast' whatever that does; but no joy.

FInding the topics above after the fact I suspect I simply should have waited longer before trying over and over.

Any, my workaound was to  switch the Deco to Static IP and cloned all the laptop settings into it.

- Preferred IP, Gateway, DNS and most importantly the MAC address (CMD> ipconfig /all).

Reboot Deco and bingo! Comcast recognized the MAC, gave it its preferred IP back and GREEN to go.

Hope this helps someone in a similar predicament,

Cheers,

Hein