Woww…looks like you’ve all shared some great tips! 
From my experience, ensuring the correct permissions and ownership for the WhatsApp directory is key when restoring backups. I’ve also found that sometimes skipping the full directory copy and focusing only on the Databases and Media folders can work just as well, as long as the folder structure is intact.
For the inverse direction (Sailfish to Android), the method mentioned by aerique** has worked for me too, just make sure storage permissions are granted before launching WhatsApp for the first time.