I know there is a section titled "General" in the Pivot Editor. This is usually set to drilldown = Yes by default, but you can select yes if it is not set that way for you also see
Splunk Pivot Drilldown Doc Here
Your question is a little broad, so I'm not sure if you are dealing with this particular problem but as a side note in case it helps you, I have had issues with drilling down into some pivots when the pivot relies on a custom regex attribute for the data. Maybe you are having that issue as well?