RAP Contract Violation: Unrequested Keys for READ BY ASSOCIATION with &1

What causes this issue?

READ BY ASSOCIATION Contract:
Entries in MAPPED, FAILED and RESULT contain always a sub-set of the
input keys. Input keys which are not part of RESULT must be part of
FAILED.

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

The contract of the following read by association operation has been
violated for entity &V2&:
The behavior implementation returned entries with a key that has not
been requested. The response must only contain entries in RESULT and
FAILED for the requested keys.
Info:
Corresponding entries in reported can be returned, but this is not
mandatory. Additional entries can be reported, referring to keys outside
of the input keys.

System Response

How to fix this error?

Please check the response of your behavior implementation and adopt it
according to the contract.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.