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What you're seeing there is a reflection artifact. To know exactly what may be causing this (as I cannot reproduce this myself yet), you can gladly send me the project file itself. Furthermore, you can briefly set the "Rendering Quality" in the Enscape Settings to "Draft", reflections will then be highly simplified and you should only see the skybox, but this way you can make sure that there aren't any gaps in the object itself, as this should also get rid of the artifact.