Whats this with Plex?, Not working at all

My MCH is set up and running fine. I‘m even connected outside my DS-Lite cable Network.
Just Plex wont work. Has been enabled 10 times already and it even shows my media a short time on the Mac web app. But It disappears after a while. It never appears on the ios App and ios Web App at all. What is all this?? What can wd and plex do to make this runing?