Field group & contains no fields

What causes this issue?

You defined a functional group without assigning any fields to it. When
you try to save such functional areas, they are deleted.

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?

It is possible to save and generate the functional area like this, but
you should really either assign fields to the functional group or
delete it altogether.

Error message extract from SAP system. Copyright SAP SE.