Error updating record with Zoho Creator Mobile App

I have a form that updates a record for an inventory app I've created. It's just a stateless form that queries a record, lets the user change a few fields, then click a button to update and makes the changes.

Running it through a web browser, it works perfectly. When I try to run the update I get an error "Error in executing update record task. Unable to update the record Assigned_To. Unable to update the value."

Assigned_To is just the first of a few records that need to get updated. It errors on whichever I try to update first in the script.

Any ideas why this might work in the browser, but not in the app?

Thanks,
Ryan