Object & & has object function "K", but no key

What causes this issue?

The request/task cannot be saved because an object entry with function
<LS>K</> does not have a key.

System Response

The system did not save the entry.
The cursor appears on the incorrect entry in the editor.

How to fix this error?

Press Enter once. This branches to the object list in the editor and
positions the cursor on the incorrect object entry.
Correct the object function or enter keys for the object entry.

Error message extract from SAP system. Copyright SAP SE.