@Miloxx 

Hi

Did you separate Deco X50-4G and X55 into two networks? Or do you have any other routers at home besides Deco?
If Deco X50-4G and X55 are on two different networks and no other routers at home, it is recommended that you set the X55 network to access point mode:
https://www.tp-link.com/support/faq/1842/
If Deco X50-4G and X55 are on the same network and your home topology is ISP router-Deco X50-4G)))(((Deco X55, in order to avoid double NAT, the following three options are for your reference:
Option 1. Remove ISP-provided router from your network
Option 2. Enable Bridge mode on the ISP-provided router.
Option 3. Set Deco X50-4G into Access Point.

Warm regards.

  @Joseph-TP X50 4g and x55's are all on the same network at the moment and there is no ISP as the internet connection is coming from the 4g sim element on the x50.  So I should set up the x50 4g and the x55s on separate networks with the x55s in access point mode?  Thanks

  @Miloxx 

Hi

Generally speaking, if you do not have an ISP router at home and Deco X50-4G and X55 are on the same network, then only Deco X50-4G will act as a DHCP server, so there will be no double NAT problem. Where did you see the Double NAT prompt?

Joseph-TP wrote

  @Miloxx 

Hi

 

Generally speaking, if you do not have an ISP router at home and Deco X50-4G and X55 are on the same network, then only Deco X50-4G will act as a DHCP server, so there will be no double NAT problem. Where did you see the Double NAT prompt?

  @Joseph-TP Ok good to know, I would have assumed that would have been a standard way of setting up the units.  Got the double nat prompt on an xbox wired to an unmanaged switch fed from the x50 4g.  Though some of my Sonos speakers are very flakey so wasn't sure if they were suffering from some kind of double addressing too