We have noticed the same issue. It is actually effecting the release date of a new application for us because the performance hit is so bad. The map performs fine until the Layer List widget is engaged, than the performance takes a severe hit, even when only the basemap is left on. This is only on map scale changes, panning the map performs as expected. Were you able to find a solution to this? Have you happened to check out any other layer lists widgets to see if the same issue is exists?
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