Have you looked at the bundled vendor script file? When bundling fails it reports the error at the top of the bundled file.
Also, I had a similar issue and found that bundling failed for toastr.js. If you remove that file from the bundle and add it regularly it might work.
You can force bundling in development by adding BundleTable.EnableOptimizations = true;
at the end of the RegisterBundles method.