There have been 2 instances of bad dice for me.
One, was over the course of a day where i lost 3 8 player escalating games based on awful dice where i would attack a stack vs stack and lose ridiculous amount of armies 2 at a time. I don't remember the exact numbers but I was 90%+ to take out an opponent and then have good odds to sweep the board in all 3 which would be like 400 points or so won.
Two, was a one on one manual freestyle game where i had held south America and was getting 7 armies per round, while my opponent was only getting 4 armies per round (for the majority of the rounds) every round we would both start our turns and he would attack me not losing a single army. Then i would have to attack back and i would lose armies. On time he attacked 2 2's with 4 total armies (15% odds to capture) and he didn't lose an army. Eventually he won the game which was awful because he though that it was a good game when in fact i had received an extra 30 armies or so over the course of the first 10 rounds of the game and still lost because of his amazing dice. (I understand this is not bad attacking but over the course of rounds 2-6ish he never lost an army when attacking me and 6-10 he had well above average dice)
Game 5962295 (with regards the the suspicion of cheating i actually asked one of the mods and they said it wasn't possible so i removed is foe although my anger is still present)
Now i understand that dice do balance over time so i must tell you about when i was in a 2 vs 2 game and it was a critical point, I had taken a bonus and the opponent hat a 15 stack that would have good odds to break my bonus. Next to his 15 stack i had a 5 stack so i decided to try to knock it down so he would be less likely to break my bonus. I then proceeded to kill all 15 of his armies only losing 1 so the dice do balance out over time.
Game 5754020