I am not really sure which can be the reason, this behavior is strange and might be a software error. I would try to reinstall the drivers, or check for updates, this is where you start from. If the problem doesn't disappear, it might be because of operating system, there is a lot of reason which can cause this. The monitor can be defect as well, you should try with another monitor, I just got recently one of the
best 144Hz Monitor Under 200 it's very impressive, a totally different experience.