OKAY! Since alot of people don't know this fix, Imma tell y'all!
So, y'know when you exit the game and later on find all your hard work/progress gone? Yeah, well, it's a simple fix. When exiting the game, DON'T just exit, instead, go to "Options", then click/tap on "Exit Game". The next time you open the app, all your progress should be saved. Keep doing such each time you wanna exit the game. This should work for any gacha club game/mod.