Node [&1]: Leaf '&3' already exists as child of node &2

What causes this issue?

The node NODEID = &V1& is a leaf and an interval node. The node name
NODENAME = '&V3& of the leaf lies within the value range [LEAFFROM -
LEAFTO] = &V4& of the interval node. This is not allowed because the
leaf and the interval node are child nodes of the same parent node
NODEID = &V2&.
Note that a maximum of 50 characters is available for message variables.
For this reason; the node name NODENAME = &V3&or the value range
[LEAFFROM - LEAFTO] = &V4& might not be displayed correctly.

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?

Try to localize the problem. If the hierarchy is loaded from an SAP
source system, you can check whether the extracted data is correct by
executing transaction RSA3 in the source system. If necessary, check if
the data is modified with a user exit. If the hierarchy is loaded from a
file, check the contents of this file. The problem might also be due to
an error in the transfer rules or in the transformation.
You can identify the two duplicate nodes from the values for the node ID
NODEID = &V1&.
The problem can be caused by identical nodes delivered more than once
from the source. It is also possible that incorrect values for
parameters such as the node name NODENAME or validity period [DATEFROM,
DATETO] are the cause of the problem.
First check if the values for the node name NODENAME = &V3& and for the
value range of the interval node {LEAFFROM - LEAFTO] = &V4& are correct.
The node name and the interval boundaries of the value range consist of
the characteristic value for the hierarchy basic characteristic and the
characteristic values of all the characteristics compounded to this
characteristic. Errors creating the node name or the interval boundaries
often result in duplicate nodes.
If the structure of the hierarchy is defined as time-dependent, the time
validity of a node can be restricted with the fields DATEFROM and
DATETO. Duplicate nodes generally do not occur if the validity intervals
of two nodes do not overlap in time. In this case, check if the fields
DATEFROM and DATETO are filled.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.