What I expected to happen was...:
To load a 1,13,2 World in the new snapshot.

What actually happened was...:
Certain chunks previously loaded had issues, such as all placed blocks within the chunks reverted back to very first loaded state (i.e.: Paths and all other placed blocks gone, segments of house disappeared). Trees on chunk borders had missing leaves, some completely missing all logs.

Edit: Since this point I've discovered that past a certain point, entire buildings are missing. This makes this issue significantly more important, in my opinion.

Steps to Reproduce:
1. Create a 1.13.2 World.
2. Load the surrounding chunks, destroy/place a bunch of blocks.
3. Load up again in latest 1.14 Snapshot.

4. There should now be chunks reset to originally spawned state.