Since the upcoming LibreOffice 6.0 version will have epub2/epub3 output support, I tested a LibreOffice 6.0 pre-release version with
a demo file originally created by Kovid Goyal to test the Calibre DOCX filter.
I wasn't exactly impressed by the output. The epub2 version had duplicate header title tags in each file and both versions had one broken link.
The converter also couldn't handle footnotes and endnotes and, most annoyingly, all generated HTML files contained inline styles.