Entries missing in table of &2 for segment &1

What causes this issue?

Entries for segment '&v1&' missing in the '&v2&' table .

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Inconsistencies of this kind can only be repaired manually.

Error message extract from SAP system. Copyright SAP SE.