[Quoth]

1) Open Office is dead. Upgrade to LibreOffice (Versions 5.x, 6.x or 7.x are OK depending on PC and OS)

2) Writer2Epub is also on older Libre Office, but now LO Writer has epub built in. It's still rubbish compared to docx to Calibre from an ODT with Save As. Last 32 bit Calibre is 5.44 and is fine for docx to epub. Even Calibre 3.44 and LO 5.x (extra docx Save As) is far better than OOWriter and Writer2Epub (XP or ancient 32 bit Linux)

3) Do edit in odt, but an extra Save As on docx format. Converting docx in Calibre works far better than odt.

4) If Calibre is on a different Computer without the same fonts, then before Save As in docx go Properties and embed the fonts.

I did use Writer2Epub on Open Office and one version of Libre Office Writer. It's rubbish compared to Sigil or Calibre (even from odt to Calibre, but an extra Save As in docx to Calibre is best).

There is a good reason both are discontinued. Don't flog a dead horse!

I've used Word (2.0a, 95, XP, 2003 & 2007), Open Office and Libre Office on Windows. Used Calibre since before 3.48 on XP.
Switched entirely to LO + Calibre on Windows, then on Linux. Maybe over 900 conversions from odt via extra docx Save As to epub, azw3 & mobi, and over 5000 conversions to epub from mobi or azw3.