Chrome on Mac - weird "can't access window controls" intermittent problem

A friend is having this problem and I don’t have the answer. When he uses Chrome on his Mac, about 10% of the time he is unable to move his mouse above the top of the Chrome user interface, thus cannot get to the Menu, Menubar, or Window Controls. He says “I then toggle back and forth between tabs or other programs, and eventually it works.” He’s pretty sure it only happens in Chrome. Any ideas?