Issue:
You have styles set up with Wipeout objects that have plotted correctly until Civil 3D 2021. Those objects now plot black (and the wipeout is not honored), when using the built-in AutoCAD PDF drivers (DWG to PDF.pc3 and AutoCAD to PDF (various flavors here).pc3 files)
Causes:
This is a currently known defect in the Civil 3D 2021 software. Autodesk Software Engineering is aware of this behavior and is investigating for a code fix in a future update. The reference ID is ACD-11504. There currently is no date as to when this defect may be corrected.
Solution:
Currently the only work around is to either use previous versions like 2020 to plot PDF’s, or to use a 3rd party PDF driver (like BlueBeam, Adobe, novaPDF, etc.)