If your printed lines are missing or faint, it is usually due to the line thickness on your drawing. When lines are set too thin, your printer cannot render them unless you increase the line weight or switch to high resolution.
Think of your printer like a screen made of a grid of tiny dots.
When CAD lines are set too thin, they are actually smaller than the width of a single printed dot. The printer doesn't know how to print "half a dot," so it skips the line entirely, making it disappear.
The Fixes:
Change the line thickness on your drawing: We recommend doing this as described on this page.
Set your printer to "High Quality" or "High Resolution": This makes the printer dots smaller and more precise, allowing ultra-fine lines to print correctly.