There is already ticket submitted for this issue, it affects all version 4.3 installs in Chrome 45+

temporary fix:

put this in your functions file:

add_action('admin_enqueue_scripts', 'chrome_fix');
function chrome_fix() {
	if ( strpos( $_SERVER['HTTP_USER_AGENT'], 'Chrome' ) !== false )
		wp_add_inline_style( 'wp-admin', '#adminmenu { transform: translateZ(0); }' );
}