I've had issues with DP cables before. Especially mini DP to normal DP. I ended up buying the shittiest cheapest cable I could find, and it worked super with my ASUS PG348Q. The more expensive cables (and the supplied cables) gave me grief with the display cutting out, not detecting. I tried the old plug/unplug/reboot/resets many many times and sometimes would work, sometimes not. In the end the really after being about to take the monitor back, I got a cheap cable, and viola.

So, not all expensive cables are good and not all cheap cables are bad.