Comment 8 for bug 1633734

If I'm reading this correctly too, the problem is the build requests aren't cleaned up from failed schedules in mitaka, and in mitaka the BuildRequest object didn't have an instance_uuid field (in the object or in the data model). That was added in newton here:

https://github.com/openstack/nova/commit/d789f6eef9052a0f8ee1987e7e3ab895581f264f

So yeah if we get to newton with any build requests which don't have instance_uuid set they are going to fail to load, or be usable. So we should have a data migration in newton that deletes any build requests that don't have an instance_uuid set as those are an indication of failed schedules from mitaka and won't work with the newton code.