Hi free associate 
I recently had the same thing non-breaking spaces showing up at as it seems random places. I didn't have time to investigate what the cause of it was, the document wasn't that long too so I fixed it (by 'manual' search and replace because sometimes it could be just erased but other times it had to be replaced by an actual space) and that was that.
But now I saw your post (and some breathing room) I thought about it a bit more.
The word-file that was given to me was created by someone who copied & pasted text from a webpage. I now had a look at the pagesource and where the non-breaking space in the word-file is there are metatags in the webpage (actually nbsp-s but also font weight changes (span style=”font-weight:normal) amongst others).
Now I don't know what the route/source of the webpage text was but somehow those codes got converted to non-breaking spaces when pasted in word.
Could it be that something similar is going on at your end?