The bug
When at the exact center of the world, the patterns formed by bedrock appear to have a sort of imperfect mirror symmetry to them, rather than the complete randomness that would be expected.
How to reproduce
Teleport yourself to 0, -59, 0
Use a fill command to clear out an air space:
/fill ~-20 ~ ~-20 ~20 ~5 ~20 air
Use a fill command to replace deepslate and other desired blocks with a lighter block to make bedrock stand out more:
/fill ~-70 ~-1 ~-70 ~70 ~-1 ~70 white_concrete replace #deepslate_ore_replaceables
Expected results
The bedrock would just be random noise.
Actual results
There is definitely visible symmetry that can be seen in the shapes the bedrock forms, with occasional imperfections.
Can confirm as of 1.18 (rc2 inc.)