Removing blank lines from Data Merge resets the paragraph style of the blank line to the style directly above it
This is version 14.0.2 of InDesign for the mac
For example, in a business card, some employees have a direct and mobile phone number, some employees only have a direct phone number. If there is a "Direct" paragraph style and a "Mobile" paragraph style, on a record where there isn't a Mobile number, after previewing the next record with both numbers the "Direct" paragraph style is now applied to the Mobile number.
The data merge should retain the paragraph styles based on the placeholders, not the previewed data.
Images I have attached:
1: placeholder view showing Direct style
2: placeholder view showing Mobile style
3: preview view showing record without mobile number
4: preview view showing next record with mobile number (both lines have "O:" instead of top have "O:" and bottom having "M:").
See https://indesignsecrets.com/data-merge-remove-unwanted-lines.php for a better description of the problem.
Hope that helps describe the issue.