Hi.
As I recall, IFC export had some issues in v17 when objects had a 3D script that generated geometry but then it didn't show in the 3D window, for instance, windows using the "use empty hole" option, or when two walls -with different BM priorities- overlapped and caused one of the walls not to show (construct in 3D, in other words) the geometry for the core.
You would need to use the session report window to check which items are causing this. It will show the GUID of each object, which you can use to search for in the IFC manager; but what I mentioned is probably the culprit.
Although you will need to know which objects are causing this, once you know, it will be easier to filter out those objects from the export.
There's another thread highlighting how to use the IFC manager for what I said.
Hope that helps a bit.