When using any terrain tool that changes heights (Rase or Lower Terrain, Set Height, Smooth height) the displayed terrain seem not to correspond to the actual one. The example below demonstrate this.
This is how it is displayed before I do anything (the tool is the height raising one).
After raising it a bit it becomes like this (had to host the images otherwhere as the limit is two):
Notice a little bump that appeared. As I understand it shows the true terrain height. However the terrain texture is not spanned over it. If you hover over the place, it’s still visible.
After holding the tool long enough the spike appears. It’s height corresponds to some discrete-like partition of my height map. So heights in between these levels are not displayed, e.g. the platform above shows the height of the next level.
Unity version is 2018.3.1f1.