Hello,
Please check the included sample Core/addTable/sample_3.php, it includes rowspan and colspan values and MS Word, LibreOffice and OpenOffice open it fine.
Maybe you are using an old version of LibreOffice? Please update to the latest version of LibreOffice (5.4 is the newest). If you are using OpenOffice you may need using OdfConverter, the support of DOCX for OpenOffice is not as good as LibreOffice.
Regards.