The "Due Invoices Reminder" dialog, which pops up when you open GnuCash if invoices are due, includes four fields: Due Date, Company, Amount, and CN? However, under the Company row what the dialog actually shows is the job name. At a minimum, this should be fixed so that Company shows the company name. Ideally, a new row would also be added to show the Job Name.
I noticed that the display of Company name for the customer is correct iff the invoice has no associated Job. If the invoice is associated with a Job, then the job name appears, as OP reports.
I submitted pull request #653 for this bug.
This has been merged into maint. Thanks!