Workflow action "Assign to user" assigns only 1st person from metadata

In the past, I have used "Create a Separate Assignment" action to assign the object to multiple people, and "Assign to User" action to assign the object to one person.

I would now like to "Assign to User" using the object's metadata -- which has 2 people in the list.

However, when I test this, the object is only Assigned To the first person. I'm able to manually add the second person but this is not ideal.

I could use the PropertyCalculator to enforce both names being added to the Assigned To property but that's also not clean.

What am I missing? Can the Workflow action only assign the object to 1 user?