Web App Designer vs Launched app have different behavior

We have a standard print widget in GC Web. The map works (with some missing features) when run in Web Designer mode, but fails when run on Launched mode. Get a bunch of 400 errors in web traffic as soon as I click the Print button: Error retrieving configurable template parameters: InvalidOperationError: 400: Print Template failed - Response Error: "undefined"

Why is this and how can we address?