Summary:
Sculk cannot appear when the mob dies on the Mud and Soul Sand. This problem arose after changing hitbox the Mud and Soul Sand blocks. When a mob dies on a complete block, a sculk can replace Mud and Soul Sand.

Steps to reproduce:

1. Create a platform of soul sand or mud.
2. Place a sculk catalyst on this platform.
3. Kill a mob near the catalyst.

Observed results:
Sculk cannot appear when the mob dies on the Mud and Soul Sand.

Expected results:
Sculk can appear when the mob dies on the Mud and Soul Sand.