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It only occurs at low speeds, 10 km or less. The bike sort of drops into the corner.
With the front wheel off the ground and the steering damper removed does it still seem notchy? If so you likely have bad head bearings, at least the bottom one. All it takes is a hard bump that bottoms the fork travel to dent the lower bearing race, hence the notchy feel. If the Cal Vin is set up properly it should handle well without the steering damper.