@SirOracle
Usually, you will barely be able to see messages flashing by in the lower left corner of your browser window but when your domestic/workplace network is slow, or your town's internet trunk is slow, or the entire country's internet is slow (eg 6pm-9pm peak) then the messages become slow enough to be visible.
That particular example makes it apparent that the Adserver has a problem. If you and it are on opposite sides of the Atlantic, for example. Our evening peak coincides with USA's lunchour, which can't be helping.