I'm not sure about the possible cause but have you tried removing the other indicators on the bottom? I have a feeling that the volume indicator moved to the top of the chart simply because there's no space for it on the bottom as that area is already occupied by RSI and that CHOP indicator (haven't heard of this one before). Try removing them and see if it changes anything. Otherwise, try to right click and reset the chart and also clear your browser cache just like other users suggested.