I recently bought 2 U2415 monitors, manufactured in Dec 2014 and daisy chained them to my laptop. I can't get them to respond after waking my laptop from sleep mode. There have been many posts on this display port sleep/wakeup issue, wasn't sure if it was affecting all monitors, or if its a cable issue,  or its a display firmware issue. I tried with different laptops and it's the same issue. I am currently using the stock cable provided by Dell.