vidmak

This. LibreOffice once erased all the footnotes in an article I was editing as a .docx. Never had such problems with .odt.

It's not just between LibreOffice and Word. Up until at least Office 2016, .docx formatting would regularly break for me between Word versions or between Office for Windows/Mac. Admittedly, Microsoft has got better with this as of late, but the .odt format is much more solid.