Inconsistent data found: Relationship(s) without object type(s)

What causes this issue?

Relationships were found with non-existent start/target object type
(data inconsistency).
These relationships are not represented on the list.

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?

Error message extract from SAP system. Copyright SAP SE.