I already am aware of this bug. I am unsure what causes it (I’ll look into for alpha -3d) but a working fix is deleting your achievement data. If you’re worried about losing it for alphas where it does work, just take the current save data out of the app data folder and put it somewhere else, then the game will create a new copy. If the new copy is also corrupt, just hit erase achievements, then load up a level. Should fix itself.