Angular 4 and SEO
The issue is not Angular4 specific. Any data generated dynamically by javascript will show first as blank, and then load its content. I assume you are looking at google page speed Insights.
To see what google see:
- comment out your external css
- comment out your external js
This will be google initial view. After that google will fetch the external files, run your javascript and render the page. Google page speed will penalize you for any changed pixels above the fold before and after fetching the external assets.
Angular Universal (or any server side rendering as this is not an angular issue) will solve that problem.
Hope that helps.