After buiding your 3D risers, raising to 3D, exporting to a Persistent Model and Navisworks successfully, your 3D riser is missing, with the exception of the skipoles

Your layers are on and the 3D_DETAIL layer is present, unlocked, thawed and visible, you just can't see the pipe and fittings.  The one customer reporting this said they disappear if the drawing is closed then re-opened.  They'll be visible in viewports as well, just not in 2D view.

See this related HydraCARD also;  https://hydracards.hydratecinc.com/cards/card-1144

When opening a 3D persistent model drawing, user gets the error and Acad crashes INTERNAL ERROR Dialog box v53.04 + v54.01

When attempting to run the NWCOUT command, you get an 'unknown command' error message;

1. Import clash errors does not work. Display Units any

When trying to export to Navis, you get this error message;

1. Navis was installed before autocad nwdout any Autocad

Date set in "options" of navis do not match version of Autocad Missing objects Navis

When in the Pipe Model Settings window (Setup window in Navis toolkit), the user cleared the text box for "Layer Name prefix" Dialog Box Acad 2016+

When attempting to create a Persistent Model, you get the error message;

Please click Apply and restart command.  Thank you.

Rinse and repeat each time

This error may start out as "Could not load default information for the Pipe Model settings"

But will then turn into an AutoCAD fatal error.

When selecting the Navis Toolkit then the SETUP button, you get the error;

AutoCAD Error Aborting

Fatal Error: Unhandled Access Violation