What causes this issue?

The normalization cannot be performed, because the product structure
contains inconsistent components.

System Response

Only an empty structure and an error message are displayed.

How to fix this error?

Execute the following steps:
Check the product structure without using any normalization.
Expand the product structure completely and check for any error messages
that appear.
Follow the instructions in the long text of the error messages to
correct the inconsistencies.

Procedure for System Administrators

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.