I have a very similar issue. My g2460pf was absolutely fine, but after I moved the dp started flickering. When i quickly move the mouse or click on something it flickers, goes black, thinks for a few and comes back. Doing this enough times loses the connection. Tried replacimg the cable with the official one that came with the monitor, no difference. Hdmi works perfectly.
My guess is the dp got damaged? Both the pc and the monitor were tightly packed into boxes and not shaken etc (moved them myself). Going to try to reinstall drivers and get a dp-hdmi switch to find which port doesn't work, the gpu's or rhe monitor's.