Why under the selection explorer, some layers are missing (no plus sign next to the DWG file) ?
The single way we found to fix it is :
1- Using Autocad, open the DWG file
2- Using Autocad, save the DWG file.
If opening the DWG in AutoCAD and resaving it clears the issue, then the program that originally wrote the DWG may be related to this issue.
What program was the DWG file created in?
Also, if you create a new file from the same program (with multiple layers), do you see the same result?
Start with some of our most frequented solutions or visit the Installation and Licensing Forum to get help installing your software.