Same problem, so annoying. I'm running chrome in fullscreen on both monitors atm just to prevent artifacts from popping up. I have noticed the glitches mostly show up on Mac OS UI elements, and chrome/vlc fex are unaffected.
fixed the glitch by deactivating "Inject Intel" in clover under graphics.
i also deactivated integrated graphic card in bios. before it was set "auto".
no more glitches, checked on both monitors more than 2 hours during heavy video tests.