Hello,
No, there's no known bug in phpdocx 8. About your question, we have checked the conversion from DOCX to PDF is working perfectly, please read the documentation available in your package in the docs folder.
The files available in this folder explain how to autogenerate the TOC. You need to add a macro to the conversion plugin (available in the same folder) and then set 'toc' as true.
Regards.