Steps to reproduce:

1) Download attached project and open in Unity
2) Make sure Vulkan is the only Graphics API in the Player Settings
3) Build and Run BugScene on a device
Observe hard edges of the light

Expected result: Smooth edge of the light
Actual result: Hard edge of the light

Reproduced with:
2019.1.0b5, 2019.2.0a1, 2019.2.0a7

Devices under testing:
Reproduced with:
VLNQA00222 Google Pixel 2 XL*, OS:9, CPU:arm64-v8a, GPU:Adreno (TM) 54
VLNQA00216 Razer Phone 2*, OS:8.1.0, CPU:arm64-v8a, GPU:Adreno (TM) 630

Not reproduced with:
VLNQA00220 Samsung Galaxy Note9, OS:8.1.0, CPU:arm64-v8a, GPU:Mali-G72

LWRP version 5.3.1