This behavior is during whole session or beginning? Because if it is beginning it is possible that there was pageload. Another case is if you are using chrome with proper extension installed? This extension (Dynatrace is asking you for installation) to load external CSS and images.
If your page is not exposing those resources public, it is not possible to download them. In such way you will se page without styling even with extension in browser.
Whole session and this is a public website, however it is an Angular, single page application. Would that have an impact? I believe I read that Angular single page applications were supported.