If a DMN Decision output is based on an Item Definition (Data Type) that consists of an object which in turn has an attribute that is a List of another type, the runner can't render the output.

Please, open the attached DMN model on the sandbox (DMN online) with runner in order to reproduce the issue.

Added to that would be helpful to add an option to show the DMN result as raw JSON. This would be helpful for more technical users (devs).