Class not returning table field when using representation?

I'm having an interesting issue at the moment.

I'm trying to call the TCWPOHTOSIGM representation and TCWPOHSIG class via the $details facet. It is not returning the supplier name though.

The supplier name exists in the table, and the field BPRNAM1 exists in the class and the representation, however it just returns an empty value.

Other fields all seem to be returning their values, as well as additional _REF fields (not sure where these are coming from???)

Has anyone experienced this issue or does anyone know the resolution?