Why do the impressions in the report not match the impressions in the data elements report?
When impression counts don’t match, here’s why:
The performance report counts each impression only once. But the data elements report counts an impression for every data element it matches. For example, if one user matches three data elements but only sees one impression, the data elements report will show 3 impressions—one for each matched element.
Because of this, the totals in the data elements report will often be higher and won’t match other reports. So, use the data elements report as a guide to relative performance, not exact impression counts.