Before this problem being resolved, a simple way to get rid of this line, in this very case, may be
0. If the PDF has been opened, close it.
1. Open the exported PDF with a text editor;
2. Search for "/BBox", there should be only one result. Here, I have the following from Line-601
<</Type/XObject
/Length 32 0 R
/FormType 1
/BBox [0 0 1180.01 804.009]
/Resources 33 0 R
/Subtype /Form
>>
3. Change the third parameter of /BBOX to a smaller one, say, 1160.01. For example:
/BBox [0 0 1160.01 804.009]
4. Save the PDF in the text editor, and reopen it in a PDF reader. (if the ghost line is still there, close the reader, and go to Step-3 again...)
