Hello,
You can transfer data including thumbnails - just check the "export also thumbnails" checkbox when exporting them (from Options page / Import backup tab).
If you want to synchronize them through the cloud, you need to enable thumbnails synchronization in the Options page / Thumbnails / "Enable automatic thumbnails synchronization".

If you have questions or idea for improvement, please write me email. I'm gonna release new version soon where thumbnails setup will be much easier.

Best regards,
Juraj Mäsiar