Reproduction steps:
1. Create a new HDRP Template project
2. Create an empty Game Object and attach a Decal Projector Component to it
3. Make sure the Decal would be visible if you were to attach a Material to the Projector
4. Create a new HDRP/Decal Material
5. Assign the Material to the Decal Projector Component

Expected result: a Decal with default HDRP/Decal Material gets rendered on the surface
Actual result: a Decal does not appear unless the Material is or has been edited

Reproducible with: HDRP 4.10.0 (2018.4.16f1), HDRP 7.1.6 (2019.3.0f1), HDRP 7.1.8 (2019.3.0f6, 2020.1.0a20)
Not reproducible with: HDRP 6.9.2 (2019.2.19f1), HDRP 7.1.5 (2019.3.0f1)

Notes:
1. Any edit to the Material makes the Decal visible
2. This is a Package regression. Regression version: HDRP 7.1.6 (tested with 2019.3.0f1)
3. A fix for the issue was applied somewhere in between HDRP 4.10.0 and HDRP 6.9.0. The issue was re-introduced in HDRP 7.1.6