Internal error during object check: Missing key, module = &1

What causes this issue?

During an internal object check, the key for the object to be checked
was not specified.

System Response

The function module &V1& (the number always specifies the Includes in
function group ITO2) cannot perform the check and therefore cancels
processing.

How to fix this error?

Make a note of the entries that led to this error. Please inform your
SAP system administrator.

Procedure for System Administrators

The error can probably be solved by an SAP program correction.

Error message extract from SAP system. Copyright SAP SE.