Why is the giving history not populating on constituent records?

This article pertains to Development 3.

This issue is typically due to there being one or more duplicate constituent records, which is indicated in the # Duplicate Constituents field on the General tab of the Constituent record.

Click the pop-out arrow on this field to open the Duplicate Constituent query which allows you to merge records as needed per this documentation.

Once the duplicate records are merged, the giving history is populated for the surviving record.