So, I just downloaded the snapshot. I create a new world and run into an invisible block. It stops me from moving but doesn't appear. You can see this in the images below. Happens both in Survival And Creative mode. When reentering the world, the blocks appear as normal until new chunks are generated.

What I expected to happen was...:
Blocks to appear as normal.

What actually happened was...:
Blocks are invisible.

Steps to Reproduce:
1. Create a new world
2. Explore a bit
3. Notice that blocks are invisible