Realm Backup Download Freezes When Almost Complete

When I attempt to download either the current state or a backup of our realm, at 4.2GB in size and over two years old, the download proceeds smoothly until it gets into the final stretch of 200mb or so, but somewhere in the last few the download bar disappears, revealing a blank prompt window and nothing for me to do but close the app. The world does not appear in my worlds after reloading. This has happened more than six times.