You'd probably be hard-pressed to put a finger on any bug there might be unless you could run a series of pure numerical tests using the generator itself, not the game. I don't know how you'd go about doing that. I just take it in stride, my "luck" with the odds runs in streaks; I once assassinated three popes in a row, all with a 40% chance to succeed, and I've also missed two different 95% chance targets on the same turn (and one assassin was even killed in the process, getting me in hot water with an "ally").