If the phone is operating correctly then the only things that should cause high standby drain is poor signal or a rogue app (not sleeping, polling frequently for updates, etc).
"Wakelocks", i.e. apps that prevent the phone sleeping, are certainly one of the things I'd be looking for, but the phone's built-in battery stats don't give you any real information on that. So at this point all I can suggest is trying a different battery monitor, e.g. GSam, and see whether it can give you more information (or maybe Wakelock Detector, if that still works on your phone and can do anything useful without root).
"Wakelocks", i.e. apps that prevent the phone sleeping, are certainly one of the things I'd be looking for, but the phone's built-in battery stats don't give you any real information on that. So at this point all I can suggest is trying a different battery monitor, e.g. GSam, and see whether it can give you more information (or maybe Wakelock Detector, if that still works on your phone and can do anything useful without root).