Classification not possible as batches have already been assigned

What causes this issue?

You cannot classify this material component as a batch has already been
assigned or batch determination has already been carried out.

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?

If a batch split was carried out, delete the split record. If no batch
split was carried out, reset the batch number.
When you have done so, you can classify the material component.

Error message extract from SAP system. Copyright SAP SE.