My girlfriend and I each have our own accounts on the xbox. Every single time we switch between our accounts, the plex app first fails to find the server, which makes us have to manually quit the app and re-launch it to find the server. Then the app asks for the username and password all over again. So as of right now there is no possible way to seamlessly use the plex app between multiple xbox accounts.
That is a known issue which is being worked on. It currently is a single-profile (hence single-account) configuration. Someone did explain how & why it was done this way initially but if memory serves, being in beta as we are, it was ok to verify/test the rest of the app. There is discussion of this in the Xbox One forum.
