Not valid primary identifier

Hello Community!
I am creating a graph from csv files, and I use values from different columns to populate classes. One column has just one value (besides blanks) and therefore it creates just one instance of that class - which is the behavior I expect. The problem starts when I want to create a relationship called "Is XYZ Company" between rows in that csv file (class Entity) and that class with one instance. When I publish the graph I get the following error as on the screen-shot.
Where can I find information on the meaning of this error? Could you help be debug this? And what is a ‘valid primary identifier’ and why it’s not ‘valid’ in this case?

Are you able to share an export of the project? If the data is sensitive, maybe you could create a small example CSV and a project with only the model concepts relevant to your question.

At a high level - Designer requires a primary identifier to be set from at least one column from the project resource. The warning is stating your mapping sa_target_nodes_and_attributes - Entity (Is [redacted] Company) does not include set a primary identifier for the class sa_target_nodes_and_attributes . If no primary identifier is set, on export or publish a warning like this is shown as no mapping will be published.