Hello,
We have tested it using MS Word 2019, MS Word 2016, MS Word 2013 and MS Word 2010; and also LibreOffice 7 and LibreOffice 6. In all cases we get a correct output, the grid lines are the same than generating a new table with MS Word.
You can send a screenshot of the output you get to contact[at]phpdocx.com . Maybe you have some extra style being applied?
Regards.