Adobe Digital Editions does not sync books across my devices

"Adobe Digital Editions 4.5.8 allows seamless fulfillment of books across devices: With this new feature, when a consumer fulfills a book on one device, the book will be automatically downloaded to all the other devices that belong to this consumer (activated using the same user ID)."

This feature doesn't work for me:

• I installed ADE on my Mac and authorised it with my Adobe ID. 'Automatically download synced books to this device' is checked.

• I also installed ADE on my Android phone and authorised it with the same ID. Auto download is enabled.

• I've added a book to my library in ADE on my Mac but it does not appear on my phone.

• I've also added a book to my library in ADE on my phone but it does not appear on my Mac.

The sync feature across devices doesn't seem to be working - can you please investigate.