If walls are not showing up entirely, that must mean that something is not lining up with your layers and drawing sets. If you’re using the native ConDoc drawing sets (see screen grab below for the drawing set to use for SU 2019), verify that you have the new drawing set for SU 2019. Or if you’re using an older version of SketchUp, you can use the standard ConDoc 4_ARCHITECT set. Try clearing out and re-loading your appropriate drawing set, and re-running Plan Generator.
You can definitively still customize the appearance and styles as you wish, and then update you scene. Can you manually turn on the “ELEMENT_Walls” layer and see if they appear in your drawing view?
Give this a try and let us know.