Unfortunately, I’ve somehow ended up with the regular weight component in the bolder weight, though there’s no layer in the component with that outline:
In case anyone else finds difficulties like this, Georg advised that the problem was caused by the smart component having an axis called ‘weight’ (because the stroke weight of that component has to vary when it’s fitting on different strokes in the other characters), but Glyphs somehow linked that axis to the main font-wide weight axis. So renaming the smart axis was the solution.