Dear Romain Barland,
Please refer to Jeremy's workaround which already mentioned in blog page: http://thebuildingcoder.typepad.com/blog/2012/09/ifc-guid-generation-and-uniqueness.html
"Answer: After some investigation we now understand the source of the issue. The GUID generation routines have an internal cache that prevents duplicate GUIDs from being generated. In IFC, these functions are called once per element, and then a call to the ExporterIFCUtils.EndExportInternal method clears this cache for the next IFC export. Please note that the first time you call these routines, they have consistent values from previous sessions.
For now, there are two workarounds:
1:Only call the functions once per session, and store their values.
2: Call ExporterIFCUtils.EndExportInternal to reset the internal cache."
Please refer to Jeremy's workaround which already mentioned in blog page: http://thebuildingcoder.typepad.com/blog/2012/09/ifc-guid-generation-and-uniqueness.html
"Answer: After some investigation we now understand the source of the issue. The GUID generation routines have an internal cache that prevents duplicate GUIDs from being generated. In IFC, these functions are called once per element, and then a call to the ExporterIFCUtils.EndExportInternal method clears this cache for the next IFC export. Please note that the first time you call these routines, they have consistent values from previous sessions.
For now, there are two workarounds:
1:Only call the functions once per session, and store their values.
2: Call ExporterIFCUtils.EndExportInternal to reset the internal cache."