Display of subcollections in collections incomplete
If there is a hierarchy of a collection with a a couple of subcollections, in the local computer all items of a collection within all subcollections are displayed in the collection. This is not the case in web-zotero, where the content of a collection within the subcollection is displayed very poorly. This is confusing.
That (non-default) option doesn't exist in the web library. The display of items isn't "incomplete" — that functionality just isn't supported there.