How to reproduce:
1. Open the “HDRPDecalLayer_repro.zip“ project in version 2022.3.57f1
2. Select the “Decal Projector“ Prefab in the Project Tab
3. In the Inspector > “Decal Layer” field tick the “Decal Layer default“ and “ground“ options
4. Close the project, upgrade it to 6000.0.37f1, and open it
5. Select the “Decal Projector“ in the Project tab
6. In the Inspector under the “Rendering Layer Mask” field untick the “Light Layer 1“ option and tick the “ground“ option
7. Enter the Prefab mode by double-clicking the “Decal Projector“ Prefab in the Project Tab
8. Expand the “Rendering Layer Mask“ field and observe

Expected results: “Decal Layer default“ and “ground“ layers stay ticked
Actual results: The “Default“ layer tick moves to “Decal Layer default“ and the “ground“ layer tick moves to “Unnamed Layer 17“ (which should not happen)

Reproducible in: 6000.0.37f1, 6000.1.0b5, 6000.2.0a2
Not reproduced in: 2022.3.57f1 (this version is used to upgrade from)

Reproduced on: Windows 11 Pro (24H2), macOS 15.3 (M2)
Not reproduced on: No other environment tested

Notes:
- When unticking the “Unnamed Layer 17“ and then ticking it back on again, the Editor will throw an “IndexOutOfRangeException: Index was outside the bounds of the array.“ error in the Console
- In 2023.3.0b1 the behavior is still faulty, but there is no “Unnamed Layer 17“