It seems like EasyEDA v6.3.22's PNG/SVG export is fairly broken. While most things work, copper areas/copper zones do not render in the TopLayer, and SolderMask layers don't seem to work at all (render empty). This seems to happen after editing any copper area's Copper to Board Outline value. After saving and restarting the entire EasyEDA application (simply re-opening the document isn't enough), the issue is fixed. This wasn't a problem prior to 6.3.22.