The Code Conversion Utility replaced a call to the specified subVI with a placeholder node.
When the Code Conversion Utility does not find a subVI, it replaces the subVI call with a placeholder node to maintain the data flow of the diagram. The most common reason that the Code Conversion Utility fails to find a subVI is that the subVI was not converted.
Review the other messages in the conversion report to determine why the subVI was not converted. If you can resolve the issue that prevents the subVI from converting in the original source code, convert the subVI and replace the placeholder node with the converted subVI. If the subVI cannot be converted, recreate the functionality of that subVI in a new subVI and replace the placeholder node with the new subVI.
If the previous suggestions don't restore the functionality of the affected code and the code isn't essential to the core functionality of your application, you can remove the portion of code. If the code is part of the core functionality of the application, you can use the VI Interop node to call your existing code, provided that the new code organization meets the architectural goals of your application. If neither solution meets the requirements of your application, do not migrate to LabVIEW NXG at this time.