Rate step &1 variant &2: data entered in fields not ready for input

What causes this issue?

In rate step maintenance, the variant characteristics determine which
of the following fields are ready for input:
Input operands
Output operands
Variant control
Line item types
Sub-transactions
Statistical rate
Period control
Optional indicator
Season
Subsequent changes to the variant characteristics can lead to problems:
it is possible in the rate that fields that are no longer ready for
input contain data. This has occurred in step &V1& with variant &v2&.
The data in the fields not ready for input has been deleted
automatically.

System Response

In the overall check of the rates, the steps with impermissible entries
were written to the error log. You must change the rates in Customizing
under <DS:SIMG._ISUBIBDRS_000030>Define Rates</>.
If you branch from there to the rate steps, the impermissible entries
are deleted automatically. If the rate contains no other errors, you
can save the rate.

How to fix this error?

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.