RE: Dell Latitude e6440 Displayport flicker e-Port replicator
Changing resolution doesn't seem to be an answer. Changing my monitor from Displayport 1.2 to 1.1, seems to fix the issue. I can't leave it as 1.1, because then the max resolution through displayport is only 2k.
So I change the monitor from Displayport 1.2 to 1.1 and then back again. This fixes it for a time until the next wakeup from sleep.
Rebooting the PC cures the issue as well.
So seems like a video driver/hardware issue on the laptop.