Greetings,
Recently I generously added new bugs to the game, one of which was causing difficulty unlocks to not be stored permanently, causing the max difficulty unlocks to be undone whenever you close the game.
This is now fixed once you update the game, but if you missed some unlocks because of this, you can simply edit your save file, which is in plain text
The file location is C:\Users\%username%\AppData\Local\One_Armed_Bandit
The file is Stats.ini. You can modify DifficultySelected, DifficultyUnlocked and MaxDifficulty values to what they should be
If you don't have them at all, add these default values to the [Unlocks] section:
DifficultyUnlocked="[1.0,1.0,1.0,1.0]"
DifficultySelected="[[0.0,0.0,0.0,0.0],[0.0,0.0,0.0,0.0],[0.0,0.0,0.0,0.0],[0.0,0.0,0.0,0.0]]"
MaxDifficulty="1.000000"
Happy gambling!