So, first make sure all instances of LibreOffice are terminated. Then try this...
cd /Applications/LibreOffice.app/Contents/MacOS && ./soffice convert-to csv --outdir ~/Desktop/csv ~/Desktop/*.xlsx
Clearly this will be possible on other platforms and may need to parameter value tweaking but you get the idea.
Load your file into ODF Validator and it will report on whether your file is valid, an interesting utility.
If you want to know what has happened to LibreOffice and see its roots back to 1985 then have a look at LibreOffice Timeline.