Hi DesuDeus, there's a tiny squashed degenerate edge right in the "pole" area of the knob, and the mesher is getting screwed up trying to deal with that.

I've attached here a reconstructed version of the knob that has that fixed, if you delete the little knob in your original object and replace it with this one you should then be able to export ok.

That should hopefully get you unblocked and get your export working for now while I continue to work on fixing the bug for the next release.

- Michael