thanks so much for investigating. i think ive tracked this down to a more fundamental problem with the renderer that manifests its self also on the browser side and how reflections are blended/composited. So i dont think this has anything to do with Native afterall (apologies for the oversight), so yes its also happening on the regular engine. Im putting together a PG right now that clearly illustrates the issue. this is good news as at least we can repro this in an environment we can both work in. 
I suspect @sebavan may have some thoughts. This thread contains hints of this issue as well. Enabling HDR in defaultPipeline disables AA