Because of "Mandatory Assignment", at least 1 assignment has to end on &

What causes this issue?

There is no assignment that ends on &V1&.
The method <ZK>ARTICLE_MANDATORY_CHECK</> of the BAdI
<ZK>BADI_MATGRP_HIER_CHK</> was used to define that an assignment to the
article hierarchy is mandatory. Consequently, at least one assignment
must be valid without gaps to &V1&. If the material was attached to
other nodes in the mean time, this requirement applies to the last
assignment.

System Response

The system cannot copy the entered assignments.

How to fix this error?

Adjust the time periods of the assignments in such a way that at least
one assignment has an uninterrupted validity period to &V1&.

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.