Ember js CLI addon using Foundation CSS complains about missing plugin

I am using an ember cli addon in another ember cli app. The addon uses Foundation CSS and when I try to run the app it complains: Error: no mixin named foundation-flex-video

This addon is used in other Ember cli apps and it does not throw this error on those apps. I have been installing/removing NPM packages in the hope of remedying this but I can't find out why the app is complaining about this mixin. It does not even use the classes that it is complaining about.