The Bug
When using the /place feature command to place the sculk vein feature, it only ever generates a tiny 2x1 of sculk vein blocks, almost always towards positive X or positive Z. This doesn't seem to constitute a 'vein', and I would expect more blocks and more variation of placement as a result.

Reproduce
/place feature minecraft:sculk_vein ~ ~ ~

Observed Result
A tiny 2x1 sculk vein appears, almost always towards the positive x or z coordinates.

Expected Result
The feature would not be so 'fixed', and have more variation, blocks, and size to it, and also without trending towards positive coordinates.