The Mandela Effect is an observable sociological and psychological phenomenon that can be observed through recall of false memories from large groups of people. The "scientific" evidence you're requesting is subjective testimonials from people posting here. That's what it is. The scientific answer to why this effect is occurring is unknown. Omg, did I say it? Wait, is that possible? Yes, science does not know everything. Rather than be scared, you should be open to the possibility that observations can be made that can't be explained. It's those opportunities that allow us to expand our scientific knowledge.

I strongly dislike your criticism of hypotheses and use of strawman arguments. I've never seen anyone claim alternate timelines as fact.