On stable stream? I believe I've fixed this on cutting edge (at least, I can't replicate with https://osu.ppy.sh/b/210619). If you're on cutting edge and experience this issue, please give me the map so I can do further testing.
Let me add on to this as well, it won't just affect long spinners, but long sliders as well
but if you click on them and highlight them, they will be fine. Only happens if they aren't selected. I believe it's not on cutting edge. The body in the timeline will appear once again once there is a certain amount of white sections on the timeline left of the slider or spinner