This question was first asked on the Dutch language section, see here.
Problem is: the document contains a table with double thin lines as borders in some of the cells. When you export to PDF, print to PDF or really print, the double lines are reduced to single ones.
This is the offending file: 16075151007995721.odt
Is this a bug, a feature or what?
If you export to PDF and put zoom to 1600% the space between the double lines can be seen.
The file content.xml said: style:border-line-width-left="0.02mm 0.04mm 0.02mm, that is 0.08 mm, or nearly 0.23 pt.
Printing 0.08 mm at 300 dpi will leave a 0.94 dot for both lines (and space).
EDIT: Setting line width to 9pt (the maximum) these are the values in content.xml.
EDIT 2: Setting the line width to 6pt and 3pt bring some surprises: the proportions of double and thin-thick medium gap remains the same.
See edited source file (border line styles.odt).
Tested with LibreOffice 6.4.7.2 (x86); OS: Windows 6.1.
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Right, I should have made more work of the math. 
Thanks a lot.
Where can I find content.xml of styles.odt? I only did find a content.xml in /usr/share/pandoc-2.9.2.1/data/odt but that file does not have a field “style:border-line-width-left”.
@BenEngbers, Make a copy, and add an extra .zip extension to your file (e.g. document.odt.zip). Open this renamed file. There is the content.xml file.