I'm having the same problem with a U2415 I bought from Amazon on Saturday, connected to a Lenovo ThinkPad 530, mini DP on the laptop to the large DP on the monitor.
Blinks a lot, was earlier showing a lot of flashing whitish horizontal bands but that went away when I reselected DP in the OSD. The blinking also seems to go away for a while if I disconnect and reconnect the mini DP on the laptop. Cannot stand this and will send it back in a day if it cannot be fixed.
What can be done?
Thanks