Blank screen in Safari Private mode

When running my app ( in Safari with private mode on both iOS and OS X, the app doesn’t load and only a blank screen is displayed.

On OS X, I sometime receive the following error in the console:

reflect-metadata shim is required when using class decorators

The app otherwise works on all major browser I tested, even in private mode: Chrome, FF, Edge, Opera,…
What can be the issue there ? Is it related to the Framework itself ?

Thanks a lot,