Screen Space Global Illumination appears really dark when using the Vulkan RHI on Windows and Linux. This behavior is also present in a Shipping build.
This was reported and tested on 4.24.1 (CL-10757647) and reproduced in Main 4.25 (CL-11062379). The results in Main are much clearer than in 4.24
Results: Screen goes dark and fuzzy (see attached)
Expected: Smooth SSGI
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-87115 in the post.