Image urls rewritten to root

I have a multisite installation using domains.
Until recently everyting worked fine.

Now I see the images on the blogs do not appear anymore.

They get uploaded to /wp-content/uploads/sites/N/
The page contains correct image url, e.g.:
http://domain.com/wp-content/uploads/sites/N/2015/03/image.png

However, when you try to open it the url gets rewritten to
http://domain.com/image.png

and, of course, you get 404 page not found error.

Any clue what could be wrong?
How to prevent rewriting?