I occasionally and randomly encounter the same issue (Chrome and IE 11 - Windows 10 machines). When it happens it sometimes continues to be a problem on any forum or page I go to, other times it doesn't persist if I navigate to another area of FT. It clears up after awhile but I haven't paid attention to whether it only fixes itself after I've restarted the browser or if it just goes away with time. If it happens again I'll make better note of the details.