A couple of ideas. If you go into RDA, do you have a section with a single field where the data may be off the right edge of the page? That might make it appear that a line is blank.
In my head, I'm thinking you've got something on a section somewhere that is cause the line to happen, but the data isn't on the page so it looks like a lot of blank lines.
You could attempt to make all of your sections Not Visible and see if the blank lines disappear from your output. Then make them visible one by one to try to figure out which section is the culprit.