Hello,
If the DOCX to be transformed uses contents or styles not supported in the native conversion plugin (supported contents and styles by the native conversion plugin are detailed on https://www.phpdocx.com/documentation/conversion-plugin/preparing-the-templates-for-its-conversion), you need to use the conversion plugin based on LibreOffice.
If you send your DOCX to contact[at]phpdocx.com we'll check it, but from the information you have posted, the solution seems to use the conversion plugin based on LibreOffice.
Regards.