In Gathering Storm SDK Assets update the human body assets (Head, Body, Hands, Arms, etc) were overhauled.
This left two sets of body parts:
1) The older parts generally ending in letters: Male_Caucasian_HeadA.ast
2) The new parts generally ending in numeric digits e.g. Male_Cauc_Head_01.ast
The older parts were left broken so that when they are opened in the Asset Previewer you get a big exclamation mark. This is because the Materials for these Assets no longer exist. This patch recreates the Materials files as the Asset, Geometry and Texture files for the older set of body parts are all still present in the pantry. There are only 5 Material .mtl files included, but this should make all the old Assets viewable.
Copy these files into the following location: ...\steamapps\common\Sid Meier's Civilization VI SDK Assets\Civ6\pantry\Materials.