System Information
Operating system: Kubuntu 18.10

Blender Version
Broken: 2.80-a30bdcc142f1 (snap)

Short description of error
Have a nested collection (pointup) in an outer collection (boxed). Instantiate the outer collection. Adding an element to the outer collection works (it shows up in the instance). Adding an element to the nested collection does not work (the new element does not show up in the instance).

Workaround.

1. drag-and-drop the new element to the outer collection and back to the inner collection
2. instantiate the outer collection after adding the new object. Delete that new instance (at this point the new element shows up)
   arrow-nested-in-box.blend812 KBDownload

In the blend file, delete the currently selected torus and add a new one. It will not show up in the instance to the right. (The nested collection (pointup) is supposed to be selected in the outliner)