When trying to split a terrain in which the heightmap is too small to divide itself into each individually split terrain you get gaps and artifacts in the split terrain sections.

Repro 1
1. Create a terrain with a Heightmap Resolution of 33x33
2. Split the terrain by 2x2

Repro 2
1. Create a terrain with a Heightmap Resolution of 65x65
2. Split the terrain by 4x4

Expected result: You get a split terrain with no artifacts or you get a warning that you're not able to split the terrain
Actuality: You get a split terrain with artifacts and gaps