In our project, we discovered that drill down cannot be done when the column width is exact same or bigger than the chart view.
Example is given: https://jsfiddle.net/YeongCY/18tmL1w1/9/.
For this example, first resize the chart area until the chart area width become very small. Then set the display unit from month to year. A column which its width is stretch to chart area can be seen. Then drill down cannot be done if the column is clicked.