Most of the netbox device types for the PowerEdge R440s parse to a valid product slug, but a few (11 to be precise) do not; The product slug parsing expects to use either the device_type as-is, or the type after stripping away -config....
Some do not match:
https://netbox.wikimedia.org/dcim/device-types/?q=PowerEdge%20R440
I'm not sure whether the Right Answer™ is to fix the device types to conform to convention, or to make the product slug parsing more sophisticated.