What is the Download Sudo History option used for?

MySudo for iOS:
If you have a lot of data in your MySudo account and transfer your account via QR code to a new device, only the most recent data is downloaded to the new device.  This is to allow the App to open quickly without delay after the QR code transfer to the new device.

If you are not seeing older messages, emails or call records come through, you can tap the "Download Sudo History" option in MySudo settings under Backup & Import/Export, which will force the App to download older history.

If you have a very high volume of data, it may take multiple downloads to sync all of your data. The app will show green text "Sudo history downloaded" if all your data has been downloaded.