That message is saying that you have multiple Network Address Translations existing in your network.
I suspect that your Xplor router is using IP addresses in the range 192.168.1.x, while your Deco X50 is using the range 192.168.68.x.
If it is possible to put the Xplor router into Bridge mode, do this. Otherwise you will have to set up port forwarding rules on both the Xplor (forward the port used to the Deco X50) and the Deco X50 (forward the port used to your NUC). See this article for more information:
If you have set one of the routers in bridge mode and there is still the MulptipleNatFound error, then i think your ISP is using CG-NAT. I think it’s CG-NAT because the router_external_ip starts with 100.
See below article
In this article you will see this:
Recognising GCNAT Address Ranges
CGNAT has its own reserved IP range between 100.64.0.0 and 100.127.255.255.
You could contact your ISP and ask the following questions (don’t made this up myself, just copied from @benjamin - Roon Staff: Technical Support).
Have you implemented carrier-grade NAT for my account level?
Have you fully implemented IPv6, or do you have IPv4 addresses available?
Can I request a static IPv4 address to support port forwarding?
Are there any ports you have reserved at the ISP level I should be aware of?