Report Analysis adding multiple subject areas (more than 2) error

Hi there, we have a scenario where we have added a new subject area to an existing report that is already set up with the Dimensionality flag, so one would assume adding a new subject area would just mean you would add the person count value into your report followed by the value/metric you wish to include out of the Person Real time subject area.

We are able to add the Person Count metric to the report without error, however when we attempt to add metric: Person Name Information 15 to the report, it errors. I have attached the error received