After drawing a line or an object in AutoCAD and assigning it a noncontinuous line type (such as dashed, dotted, zigzag, etc.), the line, or object still appears as a solid or continuous line in either model space or in the paper space viewport.
Causes:
• The linetype scale is too large or too small for the size of the affected object.
• There is a problem with the display driver on the system.
• The line type property of the line itself is Continuous, while its layer is assigned the desired linetype.
• The current annotation scale for the space is set very large or very small.
• Custom Line type (LIN file) or Hatch (PAT file) or SHX font are missing.
• Corrupted user settings.
However, "linetype scale mismatch of the affected object" is the most common reason for it.