UFF!
try it as hostrecord. (I understood that you manually blocked ex1.ddns.net on PiHole and redirected it to 0.250)
Idk how you did it but i used
pi@raspberrypi:~# pihole -a hostrecord home.mydomain.de 192.168.1.10
I have the same problem. With this command DNS requests (lan) to the hostrecord (ddns) will be answered with a specified local IP (PiHole). If you are outside you will not use the PiHole DNS so the request will be the real WAN IP.
PS: I hopped to nextcloud. I can just rate you 
Edit: Oh i saw you used Domain Redirect