I had a strange problem with the Dynamic Legend Widget v2.5 where opening the widget immediately after opening the map led to an empty legend display. Toggling the zoom, though, would reveal the legend. After some investigation, it appeared to me that the line in the function itemrenderer_dataChangeHandler in LegendItemRenderer.mxml had an awkward comparison:
As this differed from the similar line in the function updateVisibilty, I changed the map.scale comparison in the OR from <=maxscale to <=minscale as I felt is should have been, and the problem was resolved.