I tested this small demo on AMD, Intel (Windows and Mesa3D) and Qualcomm Vulkan drivers - it works normally. But on nVidia drivers it produce strange artifacts when z-buffer is not present and z-buffer update is disabled.
I attached bad.jpeg to show how it looks on nVidia drivers, normal.jpeg to show how it looks on other drivers. vk-fsray.exe - precompiled demo for Windows (x86_64).
(sorry only one picture for newly created users)
Even if I removed all ray-tracing code in the fragment shader and made it look like a just a solid color fill - it produces the same partially updated render target.