Back in the Evo days we used to call it The Harley Shuffle. At higher speeds (say, >50-mph), if you hit a bump mid-corner on a sweeper it would set up an oscillation where the tail would start waggling like a happy golden retriever. There was even an after-market device you could buy for the baggers to stabilize it.
I put a fork brace on my mid-glide frontend Dyna and that largely alleviated this “feature.” On later models Harley beefed up fork tube diameters, swingarm size and rear axle diameter, which all made a huge difference on this point, and stabilized the whole platform. AFAIK the Harley Shuffle is a thing of the past.