When items are added to the vicinity when it was empty, the selection box will not show automatically when new items are added into the vicinity.
Example:
Empty -> Item is added causing item box to show in vicinity -> selection box will not show visually however the box is over the first item in the index.
Open menu and select vicinity
Drop an item (another player will have to do this, not sure about solo)
Selection box should not show over the newly detected item however will allow you to interact with the item that is first all be it the box does not show.
The box (selection box) does show when you move within the vicinity or other containers (inventory, other storage etc).
Hopefully this was clear.