If you're using ShipBob for order fulfillment, and have noticed that items from orders are appearing as uneligible for return in Rich Returns, then please, by all means, keep your reading glasses on.
The root of this issue is lying the fact that ShipBob does not set the fulfillment status on the orders correctly. This means that the fulfillment status for all items in an order is set as null, even though the order has, in fact, been fulfilled.
Workaround: in your Rich Returns dashboard, there is an option exactly for this use case. You can find and enable it on this path: Return settings -> General -> Allow Returns for Unfulfilled Orders.