Hi Stephane,
First of all, my apologies for the very late answer.
If you have a mesh imported with the legacy importer, I recommend to use UInterchangeManager::GetInterchangeManager().ConvertImportData(Mesh, TEXT(“fbx”));
This should take care of everything including replacing the old AssetImportData with the Interchange one. It looks like this was missing.
When importing a new mesh through Interchange FBX, add your own pipeline to the default stack. This pipeline should overwrite the ExecutePostImportPipeline method where it will add your reimport pipeline to the UInterchangeAssetImportData of the newly imported mesh.
Let me know how it goes.
Thanks for your patience.
Regards,
Jean-Luc