Word processors are notorious for creating convoluted structures. I wouldn't be surprised if the lists in the headings are due to the internal structure of LO n

Word processors are notorious for creating convoluted structures. I wouldn't be surprised if the lists in the headings are due to the internal structure of LO not being easily mapped to the structure of a DOCX. Feels like a workaround for some specific issue. As I said previously, pandoc might be worth a look. But it's installation is more involved and it's able to convert everything to almost everything (it would even allow converting a LaTeX document to ePub :-) https://pandoc.org/epub.html https://pandoc.org/epub.html). But I can't really attest the quality for more complex documents. You have a working workflow and sometimes it's better to keep the devil you know instead of getting lots of unknown devils.