I regularly get questions about IFC and very often problems arise because the latest exporter is not used. This must be updated separately from Revit and for each version individually. Unfortunately, the installer is not yet available in the Autodesk desktop app, but only in the Autodesk AppStore or usually 1-2 weeks earlier on Github.
For this reason, there are now current links in the sidebar on the right - I hope these will make it easier for you to search for and find the updates!
By the way - the installed version is displayed in the IFC export dialog at the top left - if nothing is displayed here, it is the exporter supplied with Revit, which is only current until the first update in the AppStore.
German 
English