Access Point ip address is different in Web UI than what router shows

I have an Edgerouter X as router and a Fritzbox as access point. The ER-X shows a different ip address for the fritzbox than what the fritzbox itself show in its own network settings. Also the fritzbox web-ui is not reachable via the ip that ER-X is showing. For example in my case The DHCP Lease (inside ER-X UI) shows the access points ip address as 192.168.1.42 The AP web-ui is accessible (only with devices directly connected to it) via the ip 192.168.188.1 Should it be like that? I cant reach the Access Points UI with my Computer that is connected to the router, should it be also accessible

Question by hadamard on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.