In attached example, try to scroll it with mouse wheel. The Rectangle in it does not move very much and feels heavy. It is also possible to make it go a little beyond bounds and remain out of bounds. In that state, clicking the view moves it back about one pixel at a time.

This seems to be caused by pixelAligned property set for Flickable as disabling it makes it function as it used to:
Component.onCompleted: contentItem.pixelAligned=false