If you receive the message “Your device only has a Thumbnail of this photo, which can’t be edited.” when trying to edit a photo, this may mean the device you are currently using does not have the proper Sync Policy to allow for editing on your device. Editing a photo in Mylio requires a Preview or Original quality photo on the device you wish to edit on.
There are multiple ways to change the Sync Policy of a photo, folder, or even your entire device. Once Mylio has been adjusted the Sync Policy to sync a higher quality photo you will then need to connect your device to another device that currently has that higher quality for syncing to occur.
To learn more about how to adjust your media’s Sync Policy, please see this article.