Have you ever seen or hear of someone trying to type a command in the command line in Civil 3D 2015 or 2016, and it does not show up and it was working before?
For example you type plot in the command line and it does not show up or you notice it flipped to another drawings command line if you have multiple drawings open. Its act likes it's ignoring the selected drawing and typing in the command line that is in background or hidden.
This issue is usually caused by a few things either the Level of Detail is turned on in the drawing your working in and this can cause the issue or a possible corrupt user profile.
You should be able to resolve the issue by turning off the level of detail function by typing LEVELOFDETAILOFF in the command line.
If this doesn't resolve the issue then you'll need to try resetting your AutoCAD user profile.
Navigate to both these locations on your C: drive and delete the C3D 2015 or C3D 2016 folder depending on which version your trying to fix.
Then open the registry editor you can do this by going to the run prompt and type regedit then hit enter and this will pull up the registry editor
Navigate to this location in the registry editor:
For Civil 3D 2015
For Civil 3D 2016
Select and then right-click on the ACAD-F000:409 folder and choose export
(It always a good idea to back-up the registry keys your modify or deleting in case something goes wrong)
After you save the exported registry folder, delete the ACAD-F000:409 folder that you just exported
(Don't worry this folder will be recreate when you launch Civil 3D the first time)
Close the registry editor
Then launch Civil 3D and you should see the setup initializing dialog box and this is recreating the folders we just deleted and your AutoCAD profile for Civil 3D will be recreated.