Error: "There is already an entry with the same key information"

Hello SAP MDG experts,

we're facing an issue in our MDG-S project on our custom entities when they are lists. If more than one entry is added to the list, an "There is already an entry with the same key information" error is raised.

We don't know how to deal with it. We are using as reference the model entities BP_ROLE & BP_ROL_ID.

The custom entity is type 4 (Changeable via Other Entity Type; Generated Database Tables)  and the relationship with BP_HEADER entity is "Leading" type and 1:N cardinality, and a Qualiying relationship with an ID entity (ZCOMPR_ID):

BP_ROLE

Custom Entity

Thanks in advance and best regards,

Jordi