That’s due to the distance field tracing switching from “detail” which is per object to “global” which is less detailed.
I find it a really odd choice to have a single, hard cutoff between the two for reflections, as it creates this really obvious artifact. Would love to see rays start tracing back into the detail per object distance meshes once they’re close enough “inside” the solid areas of the global distance field, as then you’d know you’re close to hitting a detail mesh anyway. Would be nice as an option.
Also options for a higher resolution for the global distance mesh, maybe get a smooth transition, or at least one as smooth as possible, to less and less detail.