If your exporting the files to Google drive from within the app, it only exports the image, no layers. Your supposed to be able to export as a psd file in order to keep your layers, but I've seen some posts where that doesnt work. I'd suggest you to go into the apps files and copy/share the .tiff file from there.
Use your devices file manager, should me an app called "my files" with a folder icon. Then go to internal storage, then the auto desk folder, then sketchbooks folder. The .tiff files are your projects. Copy/share those to wherever you want to store your backups.
Then when you have to use a backup, copy it back to the sketchbook3 folder. Then you have to do some more pain in the ass stuff. To be able to actually open the back up after that, you have to go to the gallery in the app. Hit the plus button. Then pick new from image. Then my files >autodesk > sketchbooks > pick your project.
Don't know why deleting the contents of the preview or temp files would help. But if your trying to recover projects from there, they're saved as .png files, which doesnt save layers, just an image.
If your using sketchbook to make money, I'd recommend finding another app. I really like sketchbook, but autodesk doesn't seem interested in actually fixing any of the problems.
