When we scrape a public Linkedin profile, we are served with a temporary CDN URL by Linkedin which usually begins with https://media-exp... Some of our customers store the temporary CDN URL which expires in an unpredictable manner. To prevent this, we have taken to temporarily cache the images so that the links to the pictures persist in a predictable fashion. To be precise, 30 minutes.
This is by design so developers can handle images by downloading them instead of relying on unreliable CDN URLs.