[Hummingbird Pro] Does Hummingbird's cache clear when new files are uploaded?

We frequently make updates to our websites’ HTML, CSS, and JS files, and we’re using Hummingbird’s CDN to host those files. We’ve noticed that sometimes the CDN seems to automatically pick up those updated files, but other times, we have to manually clear Hummingbird’s cache.

What are the criteria for when Hummingbird updates the files in the CDN?