The Bug
Mineshafts generating in the badlands biome may generate a normal mineshaft instead of a badlands mineshaft, mainly from cave biomes generating under the surface. This causes fewer badlands mineshafts to generate.
How to Reproduce
use the seed -7985579858025862655
load up the world using default world type
teleport to -2490 -9 -2186
go up to the surface, notice its the badlands biome all around it
The Error
This mineshaft is not a badlands mineshaft, despite being in the middle of a badlands biome.
I am able to confirm this. Also affects 21w42a.