I am using Plex with a remote server shared by a friend that is accessible via Internet and a local server on my home network.
When I was using just the remote server everything worked fine, the iOS app was able to access it all the time from any network. Problems started when I added the local server.
Everything works fine when I am on my home network, both servers are accessible. When I am not at home (reproducible just by turning off Wifi and relying on mobile data) both servers show as offline and I can no longer access the remote server (which I should be, I can still access it via web UI from the same device).
To me, a developer, it looks like a bug when the iOS app cannot access the local server so it gives app on trying to access the remote server also.
This makes the app basically unusable for me.
As a “workaround” I bought the Infuse app for iOS which can access Plex servers and it works fine, I can access the remote Plex server with it all the time, proving the problem is the Plex iOS app.