On the Built-In Render pipeline, when you paint 5+ textures onto your Terrain, remove layers till you're back down to 4 or less, then trigger the Undo and Redo actions, some Terrain layers will render black.

Repro Steps:
1. Install Unity version 2022.1.0a5
2. Import the Terrain Tools Sample assets
3. Paint 5 layers of textures onto your Terrain
4. Trigger the Undo action till there are no more paint actions.
5. Continue Undo'ing actions till you only have 2 layers on the Terrain
5. Trigger the Redo action till you cannot anymore

Actual Results:
Black textures will render on the Terrain where some layers used to be

Expected Results:
Only Texture Layers currently assigned to the Terrain would render.

Reproduced on: 2021.2.0b7, 2022.1.0a5