So I figured this out, for anyone else who may happen to have the same problem. Inside our MVC/Views/Layouts folder our template has a line of code that excludes the Angular scripts if SystemManager.IsDesignMode is true.
I tried putting a seperate call in for SystemManager.IsPreviewMode - but Sitefinity doesn't differentiate the two at the same level. So having something like this did not work:
//show specific code for design mode
else if (SystemManager.IsPreviewMode)
//show specific code for preview mode
However, I was able to work around it by embedding an if/else for preview mode INSIDE the DesignMode it - so like this: