It’s likely a side effect of using screen-space reflections - the scope of the gun ‘obscures’ part of the image, and this part doesn’t show up properly in the ‘mirrored’ surface. At least that’s what I guess it is.
As to how it could be fixed - I think the SSR process should not include weapon models at all, but I don’t have any clue as to how the engine handles stuff like that.
Take note that the shape of the scope corresponds roughly to the ‘shadow’ in the lake. That’s not to say that this must be the reason for this, but switching to a scope-less gun should clear that right up?
Well, it was worth a shot. Leaves me stumped, but at least that’s off the table. Thanks for trying it tho - hope someone else chimes in with a better diagnosis.