Steps to reproduce:

1. download project and open scene
2. In project, find LightLoop.hlsl in Packages/com.unity.render-pipelines.high-definition/Runtime/Lighting/LightLoop
3. open LightLoop.hlsl and rename "ApplyDebug" to "1231231_ApplyDebug"
4. save and go back to editor window
5. observe shaders being refreshed, observe errors in console
6. clear errors
7. open LightLoop.hlsl and rename "1231231_ApplyDebug" to "ApplyDebug"
8. save and go back to editor window
9. observe shaders reimport, no errors
10a. In project, under Packages/com.unity.render-pipelines.high-definition, search "t:Shader"
10b. select all items (CTRL-A) and right click > reimport
11. observe errors persist on some shaders still
12. reimport lightloop.hlsl, reimport all shaders, observe errors are cleared now

Expected: no shader errors printed when reimporting (step 10)
Actual: some shaders are not updated (step 9) and errors are printed (step 10)

Reproduces: 2019.3.0b8 (7eb5456f98b4), 2020.1.0a8 (a932f1074310)