Items disappear from the left menu when one of these happens:

1. Its parent is removed
2. After 7 days when it does not receive data (time in days is configurable)
   Data is then removed in 1 year
   Note configured Devices in XorMon cfg persist in the menu
3. XorMon configured device removal: all its data is removed immediately
4. OS agent: it can be removed manualy

2: Configuration of removal from the UI

3: Device removal

4: OS agent removal