Bug#657515: LibreOffice Writer, non printable character not shown
I get the same trouble and it was due to some setup which was lost.
In LibreOffice, go in the Tool menu, then Options.
In the tree, open LibreOffice writer item.
Select item relative to formatting help (thrid item in my case)
- end of paragrph,
- unbreakable space,
- line feed,
and all other things you want to see.
Now non printable character can be seen.
This works for me with a french setup.