Different parent objects in diagram_info and nodes/lines/linepoints

What causes this issue?

The parent object or model in the tables diagram_info and the lines,
nodes or nodepoints table are different. You can only work on one
diagram with one call.

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.