title: Files randomly disappear from my bucket while still downloadable
body: <p>I have a mobile app from where the User is able to create a product with some photos.</p>
  <p>The logic I have implemented is as following :</p>
  <ul>
  <li>All photos are stored in Firebase Storage</li>
  <li>The product is stored in Firebase Firestore, along with the download URL of each photos</li>
  </ul>
  <p>And I'm a little confused because some of my files are not listed anymore in my bucket, <strong>while I'm still able to download them via their URL</strong>.</p>
  <p>This happens pretty randomly as sometimes it concerns very old files, and sometimes very recent files.</p>
  <p>Is it the right way to attach Storage files to Firestore documents ?
  What am I possibly missing here ?</p>