I've played all the way through the game and didn't find anything unusual about the dice rolls for or against the player. Across an entire game i didn't see a single double 20 on an advantadge/disadvantadge roll, which with the number of paired rolls taken was a bit of a fluke, i would have exspected 1-2 based on the sheer volume of rolls and odds of 1:400. I saw a single double 1 on an advantaged attack roll, by one of my characters. Some streaks both for and against me, but nothing exceptional that made me think the dice are cooked. People in general are really really really bad at evaluating randomness of results. If you have a specific conjecture about how the dice are bad I might go to the effort of testing it, but testing the dice in every possible way is just too much work without some way to automate logging and parsing the data.
Based on your angry posts, it seems like you feel the dice are weighted to a non uniform distribution against the player. One could also interpertet your complaint as "the dice are biased against the side in combat that is currently winning to make the combat more challenging". That is a lot more difficult to test becuase you have to decide how the game thinks a side is winning and if its a hard on/off or escleating soft bias based on current balance/inbalance of forces. I can test if the dice are continuously biased for or against the player easily enough, either as a whole or only in combat to your preference. I cant' really test if you think the dice are biased in either direction based on who is subjectively "winning" at the moment. Its possible that either by design or by error the dice are cooked, but if so it isn't badly enough for me to notice in an entire play though of the game.
make sure you check your settings there a few different options for "loaded" dice and of course the option for 'true random', however, there is no way a computer can be truly random but close enough that you should not really notice.
it seems to behave just like in an in person game with physical dice. sometimes i have unbelievable good luck and sometimes i can't roll double digits on a d20 all night long
My experience with the dice is that if you push your AC values very high, even with "True Random" as the dice setting, the enemies start to roll higher to compensate. This could be coincidental, but then I must have had the strangest flukes. As in plural. Here's an example of my experience:
I ran a fight with some elementals in the Lava Forest. My party consisted of a Shadowcaster Rogue, a Mountaineer Fighter, a Greenmage and a Cleric (Oblivion, I believe). My Fighter had a very high AC. Plate +1 (AC 19), Shield +2 (23), defense style (24), the Abjuration ring of protection (25), Shield of Faith from the Cleric (27), Haste from the Wizard (29) and the Mountaineer subclass bonus for a total of 31 AC. An absolutely absurd value to have, but that's how it is. The highest To Hit bonus on an enemy in that fight, IIRC, was +9 or +10, meaning they could not land a hit on the Fighter without a critical hit. On top of that, I put Protection from Evil and Good from the Rogue on her since all enemies in the fight were elementals, meaning all attacks had disadvantage.
I had to do the combat twice, because the first time the Fighter was focused fired to death, receiving crit after crit from the enemies, stacking their burning damage DoT. My Fighter was a Hill Dwarf with 18 Constitution, so they had ~90 HP at lvl 8. The second time I tried the fight, I was crit a bit less, but the Fighter still left the fight with less than half HP.
It is entirely possible that this was just a fluke, but it seems somewhat unlikely. Each attack against the Fighter had a 1 in 400 chance to land at all and they were hit ~15-20 times over the course of 2 back to back fights. I did double check and the setting was "True Random" and no random seed preserved.
The late game with the Mountaineer Fighter (at least up until where I played) was less extreme examples of the same trend: Enemies landing hits through high AC values with suspicious frequency. With characters who were not as tanky, however, I did not have the same issue, both in the same party and later parties.
In short? My impression is that if you stack your AC too high for the enemies to deal with, the game compensates for it by cheating the dice. That could be a fluke, but it sure seems to happen a lot if you get too many high AC items and features on a character.