To my experience, the problem is the slide in bullet connectors, where the sleeve portion of the connector is wallowed out to too large a size, not making contact with the bullet part. I suspect that heat under the tank may even contribute to the sizing disparity.
I had the same symptoms. Full left thunk on the bars resulted in a start. Cleaned the two connectors that the sidestand switch wires run through (under the tank, left side of frame) and no more starting trouble.