When there is a large number of stacked by values on a bar chart, the drill down doesn't work properly. Clicking on some of the colored areas does nothing while it is working for other colored areas.
It is hard to reproduce it in OOB as you need a lot of data. Basically you need to create a Bar report against a table with a lot of data and use a Stacked by field which will return a lot of Stacked by values. Run the report and notice that clicking on some of the colored areas does nothing while it is working for other colored areas.
There are two possible workarounds: