I have a designed a map using a scaled simple marker symbol. It is a rule-based design and symbol scaling is done by the siye assistant based on a field value for any of the rules in the same way. Everything works fine within the the map - legend / table of contents symbols are scaled according to map scale, within the print composer / item properties-window symbol scaling works fine as well.
However, the legend of my map-layout doesn't show any symbols.
Strange: changing scales in the layout (via map/item properties/scale) changes line spacing of my map-legend - indicating that there is information about how to scale symbols somewhere in the background.
... but the symbols remain invisible in the map-legend. Does anyone have any ideas?
QGIS 3.2 Mac and Windows.
@tallistroan seems that there is a serious problem in version 3.2 ... following your workaround description resulted in correct scaled symbols on the map and ugly results in both the Advanced > Data-defined Size Legend tool and the composer legend. obviously the sizes do not correspond to the map scale and to symbol sizes within the map.