If I do the entire Spire in one session (and I don't recommend this for various reasons), I have noticed that I tend to get the same rewards over and over. I got 4 artifacts from one Spire once. I have a friend who has twice got 3 artifacts just doing the first boss.
I'd be interested to hear if anyone else has noticed this or if I'm seeing something that isn't there.
Granted it's been decades since I did any coding, but when I did (BASIC, Fortran IV, and Pascal), it was a common failing of RNGs to get "stuck" on the same number range. If you generated 100 "random" numbers between 1 and 100, you would usually see a place where there were 5-6 numbers in a row with very close values e.g. 2,6,4,3,6 while the rest of the results looked more like what one would expect.