You haven't mentioned any cables, resolutions or GPU.
The monitor is 2560x1440 at 165Hz. Are you running it at that? Is it straight from the GPU, or does it go through a dock? Are you on a desktop, tablet, laptop?
Does it work at 1080p60? 720p60?
Might be a crappy DP cable, and disabling the device in device manager is actually disabling extra features or AMD FreeSync or whatever, so its going back to being a dumb display