Cannot replace world for new or existing realms

I am unable to replace the world for my realm. When I try to do this, the progress bar for the "Uploading World" dialog moves to 100% and then hangs infinitely. It doesn't matter how long I leave my devices in this state, the upload never completes.

I have tried:

• Resetting the world – this works

On a realm purchased via iOS:

• Replacing the world on my iPhone 6s Plus with an existing, used world – hangs
• Replacing the world on my iPhone 6s Plus with a newly generated world – hangs
• Replacing the world on my Windows 10 Pro computer with an existing, used world – hangs
• Replacing the world on my Windows 10 Pro computer with a newly generated world – hangs

On a(nother) realm purchased via Windows 10:

• Replacing the world on my iPhone 6s Plus with an existing, used world – hangs
• Replacing the world on my iPhone 6s Plus with a newly generated world – hangs
• Replacing the world on my Windows 10 Pro computer with an existing, used world – hangs
• Replacing the world on my Windows 10 Pro computer with a newly generated world – hangs

NOTE: This has all been attempted with my own Xbox Live account, no others. My Xbox Live account is the same as the email address for my user account on this bug tracker.