Depending on Internet connectivity this could take an extended period of time, particularly when projects for off-line use are downloaded for the first time. The device going to sleep while performing a download can cause issues which result in the download on completing successfully.
The following steps/setting should be invoked to ensure that the device stays awake during the data synchronisation process:
On IOS Devices:
On Android:
This process involves enabling Developer Mode. If you do not have full administrator permissions on your device, you may not be able to perform the following steps.