Looks like Lumen reflections honestly, I’ve never seen SSR in Unreal take into account surface roughness, much less do contact hardening for reflections. It just fades SSR out at the roughness increases.
(Edit: Looks like SSR can account for surface roughness when using the experimental denoiser)
Anyway, if this is indeed SSR; SSR falls back to the reflection captures, if there are no reflection captures it will fall back to the skylight. Solution: Place reflection captures.