Custom Web Component Reference Error

I have created a project that uses a custom Polymer 3 wrapper around the Muuri.js file. When I launch my polymer project using “polymer serve --open” the project executes fine. However when I attempt to launch the Vaadin component that wraps the JSModule, the internal polymer 3 wrapper throws an Reference Exception trying to instantiate the Muuri constructor from the inner muuri.js file. I have no idea why muuri.js would be found (i.e. no 404) but the instantiation throws a reference exception.

I have attached my project as well as a screen shot of the problem…

Can someone please help?..this is really confusing. (451 KB)