Reproduction steps:
1. Download and open the attached project "VertAttr_Vulkan_Issue.zip"
2. Build and run for Android

Expected result: The rendered Mesh is green
Actual result: The rendered Mesh is black

Reproducible with:2019.4.19f1

Reproducible with graphics API: Vulkan
Not reproducible with graphics APIs: OpenGLES2, OpenGLES3

Reproducible on:
VLNQA00321, Xiaomi MI 9 (MI 9), Android 10, CPU: Snapdragon 855 SM8150, GPU: Adreno (TM) 640
Google Pixel 2XL (reported by the customer)
Google Pixel 3 (reported by the customer)
Google Pixel 4a (reported by the customer)
LG V40 ThinQ (reported by the customer)
Moto G Fast (reported by the customer)
Xiaomi MI 6 (reported by the customer)
Xiaomi MI 5 (reported by the customer)

Not reproducible on:
VLNQA00122, Samsung Galaxy S9 (SM-G960F), Android 10, CPU: NOT FOUND, GPU: Mali-G72
Samsung Galaxy S7 (International Version; Exynos chipset) (reported by the customer)
Samsung Galaxy S8+ (International Version; Exynos chipset) (reported by the customer)
Huawei Mate9 (reported by the customer)
iPad 9.7" 6th gen (14.3)
iPad Air 2 (11.0.3)
iPhone XR (13.4.1)
iPhone 8 Plus (12.0)

Notes:
Could not test on other Unity streams as the project uses a custom shader which breaks when changing versions (see edit for the error)