Sometimes, I'll open Plex inside my home and it connects to the server successfully. But then later when I open it again from outside my home with no Wifi or even no signal at all, it gets stuck trying to reconnect to the server, with a spinner in the middle of the interface.
Most of the time when I open Plex and I know I won't be able to connect, because I'm underground in the subway for example, it's because I'm trying to access content that has already been synced to my phone.
So why does it need to connect? I can go around this by closing the app and starting it again. But still, a bit annoying to have to do that every time.