I have massive lag and stuttering on the desktop on which ever monitor is not set to primary. If I check the box to make monitor 2 primary, monitor 1 stutters. If I set monitor 1 as primary, monitor 2 stutters. It is purely determined by the primary setting and no other setting such as refresh rate needs to be changed. I never had the problem before. I just enabled both displays simultaneously after a very long time and noticed it's broken now.