Line breaks (line endings) disappear when the document is merged?
If a Line Ending character is included inside a text link, the Line Ending character will be removed because incoming variable data will replace all of the characters that are inside the text link, including the Line Ending character.
There are several ways to move a Line Ending character to the outside of a text link. For example,one easy way to repair this, simply highlight/select the line ending character and nothing else, then open the "DesignMerge" menu and select "Utilities > Link > Clear Selection Range."
TIP: DesignMerge will automatically exclude non-printing characters, such as a Line Ending character, that are at the beginning or end of your selected text from being placed inside a new or replaced text link if you turn on the Smart Tags preference (open the DesignMerge menu and select Preferences to access this preference).
To confirm no line endings have been inadvertently included inside text links, place your text cursor inside the text frame that contains text links and then use the Previous and/or Next buttons on the DesignMerge palette to have DesignMerge select all of the text that is inside each link in the box.
Also, when entering text in a box where text links have already been inserted, you will want to remember that InDesign will automatically include text that you enter immediately following a text link inside that text link and also InDesign will automatically include text that you enter immediately preceding a text link that is at the beginning of a line inside that text link.