I did not say it was because of eye adaptation. When certain “conditions” are not met on a surface, Lumen resorts to SSGI and essentially turns the bounce lighring off when light part of a surface is not in view.
You can view what surface will and will not bounce light even when off screen by turning on Visualization / Lumen Scene, then input the console command ‘r.Lumen.DirectLighting.ForceOffscreenShadowing 1’
He explained and demoed it during the stream right when the editor crashed on him. It’s also mentioned here at the very bottom of the page: “Mismatch Between Shadow Maps and Ray-Traced Shadows” Lumen Technical Details | Unreal Engine Documentation