Hi,
If there is nothing scheduled, your device should display the default layout.
When you schedule a layout, your device should ‘know’ about it after next collection interval then download new content(if necessary) and update schedule. Each collection interval client exchanges informations with CMS - How do Players communicate with the CMS
There are some things that can interfere with schedule for example causing it to miss scheduled layout.
The Most common cause for this behaviour would be really long media durations on your current/default layout.
So you might want to look at that, also this for explanation - Understanding Media Duration and how it affects the playback of a Layout
If you won’t notice anything like that on your layouts, could you please show us a screenshot of status window on your client when the issue occurs? (press ‘i’ on your keyboard when Xibo has focus to display status window)