Have a movable marker in line series which will stay on position even if the data is loading dynamically.
A marker like a tooltip but which will stay all the time and can be moved around on a line series chart. This marker should not disappear even if the line series data is updated.
Thanks for sharing the idea, but I'm not quite sure how this should work.
Did you try using separate series (scatter) with just one point? Or an annotation that can be dragged around?