When applying physics to a VoxelMesh, it works as expected. But if a single Voxel on the Mesh is the water material, it will disable collision on the entire mesh causing it to fall through the ground.
How to reproduce:
Create VoxelMesh of Large box. Enable Physics and Collision. Drop from a good distance and It will collide with the terrain mesh as expected.
Create a small VoxelMesh using the Water material, and place it on the Large Box. Merge Meshes. Drop from a good Distance, it will fall through the terrain mesh.
Thanks!,
Novalok