I have set up dynamic DNS with tplinkdns but the address is inconsistent with my current WAN IP.

According to the Deco App, my WAN IP is a.b.c.d.

However, if I am using a service such as myipDOTcom, another IP address gets listed (say q.r.s.t), which corresponds to the tplinkdns address resolution.

Now, trying to access services on my network at q.r.s.t fails, but when using a.b.c.d I do get access from "outside".

I am wondering two things: why the WAN IP is different than the apparent external IP, and why only one seems to correctly forward?