How to reproduce:
1. Create a new LWRP/Universal RP template project
2. In the Project Browser, add new material
3. Drag material icon (Project Browser) onto 'ground' (Scene View) (so it can be seen easily)
4. Ensure material is selected in the Project Browser
5. In the Inspector, select a normal map texture

Expected result: Normal Map is applied to Material
Actual result: Normal Map is not applied to Material although Normal Map Preview is shown in the Inspector

Reproducible with: 2019.3.0a10 (URP 7.0.0), 2020.1.0a14 (URP 7.1.5)
Not reproducible with: 2019.3.0a10 (LWRP 6.5.3)

Notes:
1. Not reproducible with Base Map;
2. If you click on Material in Project Browser after assigning Texture Map or assign Base Map before other Texture Maps, Material updates and Texture Maps are applied immediately
3. Not reproducible with HDRP, Built-in pipeline
4. Not reproducible on macOS, reproducible on Windows and it's build
5. Reproducible with URP/Lit, URP/Baked Lit Shaders
6. Video of reproduction attached in Edit
7. Only occurs when changing normal map from None to a texture, if there is already a normal map selected, there is no issue
8. The material can get stuck without a normal map if the "refresh" is not forced by selecting the material; even after restarting or building player