Reproduction steps:
1. Open attached project "Shape_Interpolation"
2. Open "Scene"
3. Check that Spline is being interpolated Continuously
4. Check edges roughly at "Here", "And here" Gameobject locations

Expected result: Height is interpolated continuously resulting in a smooth transition
Actual result: Height is interpolated linearly resulting in sharp spike-like bumps

Reproducible with: 3.0.14 (2019.4.11f1), 4.0.3 (2020.1.0b5), 5.0.2 (2020.2.0b4)
Could not test with: 2018.4 (Errors when importing package)