du:math/random_seeded only returns a handful of values for an unknown reason. If the value is small, such as 4. then it only returns one value (in this case 1), and if larger, then it repeats a small selection. Of note is that this method uses a linear congruential generator, and while Cave Biomes' seeded pRNG also does, the function there does give the expected output. Important for structure generation, as only one (or few) structure(s) of a given size type will actually be generated.

Fixed in 2.1.3