My New PX 277 monitor seemed like it was working fine. That is until Radeon Software crashed randomly without warning. After the crash Windows wouldn't recognize that my monitor was 144Hz. It only listed 30/60Hz available. I went into Radeon Settings and it recognized my monitor only as a 60Hz monitor too when it is in fact 144Hz. I tried everything from uninstalling drivers to changing my Display Port cable but the issue remains.
I don't know if this is your issue or not, but Windows updates has a habit of replacing specific monitor drivers from your manufacturer and replacing them with the Generic PNP. If you don't have a specific manufacturer supplied driver. Check on you manufacturers site and get one if it exist. If one doesn't exist, it likely works fine with the Generic PNP driver. I had to disable Windows 10 updates from downloading drivers to stop it from changing my monitor driver on me.
Also go to Device Manager and make sure the settings for your "Hz" aren't being limited there. Sometimes that gets set at 60 then the graphics driver doesn't pickup that 144 is available.