title: Background Fetch not working on all devices
body: <p>In a test device that's never been used for development, 
  iOS Background Fetch works fine, continuing during the night.</p>
  
  <p>But on two other devices, used for development, the fetches sometimes occur, but often don't, not even during the night.</p>
  
  <p>Did anyone experience the same odd behaviour? Do fetches occur only when there's Wi-Fi available, or are there other factors I might be missing that influences fetch behaviour?</p>