Hi,
That is really weird as Tekla BIMsight has much older import plugins. Oh, which one you have installed last? Tekla BIMsight or Trimble Connect Desktop? Both software are sharing the import plugins.
If Tekla BIMsight, then please uninstall Trimble Connect Desktop and install it again.
Trimble Connect Desktop cannot load ifc models using the import plugin that comes with Tekla BIMsight 1.9.9.
Hopefully this helps.
Best regards,
Marko Myllymaa
PS. You should always install Trimble Connect Desktop after the Tekla BIMsight.