Search engines like google don’t index 4XX pages given that they don’t function. Because of this, they’ll disregard any canonical tags pointing to these kinds of pages and sometimes wind up indexing the wrong (non-canonical) version of the web page. Hreflang tag #one could well be the self-referencing entry in this https://growthbookmarks.com/story18753720/5-tips-about-hreflang-not-using-canonical-you-can-use-today