Number of eliminated duplicates = &

What causes this issue?

Shortening the primary key involves a table conversion via data
unloading and loading back. Because the primary key was shortened,
duplicates may occur in the new table.

System Response

All duplicates are removed from the table. The system determines which
duplicates are removed. Here only the number of eliminated duplicates
is specified.

How to fix this error?

Shortening keys should be carefully planned, as data can be lost
when the duplicates are eliminated.

Error message extract from SAP system. Copyright SAP SE.