Since the title says "Can't Fix": Isn't it fixable by injecting some entropy into the PRNG for every roll like button press durations in nanoseconds, temperature, hardware quantum based, ...?
Not to mention full regression testing on the statistics of the game. You would have to "re-prove" the validity of the RNG , which requires another QA cycle, statistical expert, and game designer (to ensure that the frequency and distribution of wins matches the specification sheet)
But what would be the difference with other casino software bugs then, are those also "Unfixable" then?
If they are related to money, they pull the machine out of the field until a new software version is fixed. A gaming company I used to work at had an issue with multi-jurisdictional machines that worked in Mexico but could display english or spanish. The machines could also change denomination, say from $0.05 to $0.25. There was some bug where if you reset the power, you could get it to bump your credits up from 20 nickels to 20 quarters (or might have been 20 pesos to 20 cents), it was something dramatic and easily exploitable that was fixed promptly.