Required Reading
There is a bug in Checkpoint where save backups do not appear in Checkpoint. This issue can be resolved by these checks:
Troubleshooting
Make sure that the saves are in the correct place.
All Checkpoint backups should be located in \3ds\Checkpoint\saves\{some hex code then the name of the app}/{The name of the backup. This does not matter as long as it uses legal characters}. Make a backup of save of the app you are trying to restore even if the path name is correct. (You won't use this, it just creates the correct folder diagram for the backups), then move the file(s) that contains the save into the created folder and replace the new backup that I stated we won't be using.
Make sure that the save isn't corrupted.
If you look at the save in notepad, it will look corrupted even if it's not. If the above step didn't work then there is a good chance your backup is corrupted.