I have known since its inception that Ancestry is not a reliable source for tracing family lineage, so you can imagine my frustration when people still use it and say they found out they are X, Y, and Z. Even despite several investigative news reports coming to the surface, Ancestry and services like it continue to grow in popularity and rewrite peoples' history. To address this, they always fall back on their "limited scientific capabilities," but it should be noted that most of them only analyze a fraction of each DNA sample and don't share their data with anyone, which makes it by definition unscientific.
CBC: Twins - 5 DNA ancestry kits, all different results
CBC Twins YouTube Video
Tufts University: Pulling Back the Curtain on DNA Ancestry Tests