Universal version of this bug:
https://fogbugz.unity3d.com/f/cases/1187428/
As Universal did not support terrain height blending until the version where it was made to not work correctly, this version of the bug is not a regression and thus a fix is less urgent.

Repro steps:
1. Use a project with Universal 7.0.1 or higher
2. Go to the asset store and download "Terrain Tools Sample Asset Pack" from Unity Technologies (it's free) and import all contents to your project
3. Create a material with shader "Universal Render Pipeline/Terrain/Lit" for Universal
4. Enable height based blend on the material
5. Create a terrain, go into the terrain settings, and set the material to your new material
6. Go to "paint terrain" tools, choose "paint texture" from the menu
7. Add 2 of your existing terrain layers through "edit terrain layers", the layers should be "rock" and "snow"
8. Fill a large portion of the terrain with rock
9. Choose the soft brush, choose the snow layer, and click once on the terrain
10. Go to your terrain material and drag the slider from "0" to "1" and back

Expected result: for the best looking behavior and to maintain parity with 19.2, the terrain should interpolate blending with a fully height based blend at 0, a fully "lerp" based blend at 1, and at any point in the middle, varying degrees of soft height map based blend (when fixing, make sure to do these steps in 19.2 HDRP to see what the correct behavior should be)
Actual result. The blend does a full "lerp" based blend at 0, something almost identical looking at 1, and in the middle, varying degrees of very bad looking blending that don't look anything like expected behavior.
See attached images for expected versus actual result.
ADDENDUM: Unlike HDRP, Universal also has large edge aliasing problems with mixing certain layers together. This will also need to be fixed, if fixing for parity does not solve this. See attached image. Placing the "Sand" layer on the "Rock" layer with a soft brush (one click) and then moving the height blend up and down will repro this problem.