Well, to question the RNG we have to first understand how it works. Many computers do not actually have hardware to generate random numbers. Instead, they are pseudo random generated through either simple or complex algorithms (such as that of rand() used in the C library). In order to keep it from generating the same numbers over and over, time is often used as the rand seed.
Another common way to generate random numbers is by measuring CPU cycles/ticks. I.e.
GetTickCount. Because the processor is regulated frequently, this will almost always return a different number. Diablo II happens to use both methods for its' RNG.
First when the game is opened, the random seed is set based on the current time. Whenever you actually create a game, a "game seed" is generated for that session. That helps keep things even more random within the already random map seed. The next part is going to depend on the patch. Prior to 1.09, it appears only the map seed is used in determining monster spawn points. As we've known for awhile, racks are
only influenced by rack location and sprite spawn points. Every time a monster spawns in its' "active" radius, the rack gets reseeded or "refreshed" by the code responsible for updating the sprite table. Going back even further, prior to 1.07 it appears loot dropping was also only affected by map seed. This allowed for legitimate "dupe" items a.k.a monsters can sometimes drop identical rares if killed the same way (time+location).
Now in the current patch, I've noticed more calls in various loops to return the processor speed. It seems whenever you make a game, the game seed, map seed, and processor speed are all factored. The latter is the most random of the three, and is likely responsible for the unpredictable nature of monster spawn points. This amounts to changing racks more often, of course some racks will be semi-stable on occasion due to monsters being disallowed to spawn on certain tiles.
With that being said, I've had some maps where it takes 10 runs to see a gold, others thousands with nothing to show for. In the process of searching for racks, I often get one or two random unique items--usually useless although I did rack a random Arreats' before. That alone would convince me that rack quality is much more random than the rack itself. But it's no doubt that time is likely the biggest factor here. If you could "freeze" your computer's CMOS and the rack dropped more consistent, that would give us a big clue.
TLDR -> Quantum computers for the win!! They react to noise, perceiving decibels, frequency, bit rate, and patterns as machine processor instructions! They would use white noise to generate random numbers, which is basically impossible to predict and can be intercepted in practically an infinite number of ways. Imagine your girlfriend walks in to yell at you for spending too much time on D2. Then in that moment, her voice triggers an RNG change which happens to leave a Zod lying in front of you.
Sorry, but I'm busy playing video games hahaha!