I’m having the same problem on my Android phone as well as my NVidia Shield.
On the Phone
Starting the app after a while of not using (12+ hours) I get server not found errors. All I have to do is select another Library and it connects to the server.
On the Nvidia Shield
The shield has a display which shows the recently watched items for a particular app (e.g. Plex, Netflix etc). Plex used to be in this display showing the up next and continue watching items. It is now dropping out of this display with a notice saying that communication with the service was lost. However if I start the Plex App it repopulates into the menu. The Shield connects all the time to the server.
It would appear that there is some sort of disconnect between the server and the apps after some sort of time out period.
