Hi Gysbert, that was very strange.
The number of items/bars is 28 within the chart - the "Max Visible Number" or "When Number of Items Exceeds" (which is what I assumed was the same thing) was set to 10.
It wasn't until I reduced it to 5 that the scroll bar appeared! I then reset the number to 10 and the scroll bar stay.
Not sure why but that worked.