I think you're being downvoted because this is when the placing algorithm is still running - it's going down the diagram and using what looks like a genetic algorithm to determine the best placing for the labels.
It's terrible UX. Why do I care that the algo is still running while the window is scrolling? Detect the scroll event and pause the algo. Anyway, it's not fit for displaying a a lot of events, so that should be noted. The resulting diagram is incomprehensible. I'm talking data vis basics here, not being clever. C'mon.
Even the demo UI gives you the options to stop it from showing the intermediate steps, so your complaint is mostly that the demo doesn't magically pick the best parameters but lets you play with them?
That wasn't obvious from first use and at any rate the resulting diagram for anything above a trivial number of labels is incomprehensible. So magucally arranging labels is not really scalable. You need a differemt visualization model. That should be stated and made clear up front.