It might help as well if you can post screenshots of your SyncBack OnInsert settings (that's not working) as well as Windows Explorer which shows clearly the external hard drive volume label (name) so that we can compare to make sure the name is correctly set, etc.
Also, post a picture of your Modify > Simple setting page to show your Source/Destination paths.
Also, post a picture of your Modify > Simple setting page to show your Source/Destination paths.