Structure explosion for item & is not possible

What causes this issue?

You have tried to carry out a structure explosion within an exploded
structure, but this is not possible.
For example, the system finds one component and one item category
within an exploded BOM that leads to another BOM explosion in document
processing. This is not possible because you can only explode a multi-
level BOM and the explosion can only start with a document item that
has not been generated by the previous explosion.
Similar problems occur when combining BoM explosion and product
selection.

System Response

The system does not carry out the lower-level explosion.

How to fix this error?

Configure the settings in Customizing, so that sub-items do not lead to
another explosion. It might be that the wrong item category was
determined for the sub-item.

Error message extract from SAP system. Copyright SAP SE.