I don't know much about Angular, just enough to get by, but I know all about nginx & CORS issues on multiple webserver/configurations. While this issue can likely be fixed from within the angular project, we can also fix it at webserver level (I assume you know this as you detailed NGINX in your job description).
Just a rough guess, but I also assume your problem has to do with the CORS header being set multiple times which cancels it out, thus causing mixed content issues and breaking your HTTPS layer in the browser. It's possible both nginx and your angular project are including this header. Probably not, I have no way of knowing for sure until I look, but this is a common occurance. Either way let's chat, I'd love to solve this for you.
And even if we don't chat, try removing the setting of this header from either NGINX or Angular, and vice versa, while keeping an eye on the chrome debugger console during the page load so you can get an idea of what is happening.