Broken screen substrate
. Your Gen3 has unquestionably suffered some kind of mechanical impact - the substrate doesn't break spontaneously; it's a physical breakage, not an "electronic" problem. It's not covered by the warranty - Bookeen will charge you €120 to replace the screen.
You can at least look on the bright side that is it repairable. If you did the same thing to a Kindle, you'd have to throw the whole thing in the garbage, because Amazon don't offer a repair service.