The Idolm@ster SP: Wandering Star

[[Unknown]]

Most likely you are playing a hacked game which was modified to be compatible with older PSP firmware. Around those versions, PPSSPP was changed to save in a way that more properly matched actual PSPs.

There are a few options:
1. You can try the original (unhacked) game. It may load the data properly.
2. You can try creating a savestate in the game and loading it in the new version, then saving.

-[Unknown]