My one and only Mandela effect experience (that I'm absolutely certain of) (and even that, not 100%)...anyone seen the Bond film "Moonraker"? The scene where jaws meets the little blond girl...he smiles at her...she smiles back, revealing a mouhtful of braces...matching his metallic maw. Except....not. Apparently she no longer has braces, or never did...(!?!)
If.....IF....I HAD to come up with a prosaic explanation for this (and many other Mandelas) at gunpoint, it would be this: We watched that scene, and FULLY EXPECTED the girl to have braces. It was such an obvious gimmick, that when it failed to materialize, we went over it and over it in our minds, wondering how the hell a Hollywood director - heck, ANYONE with half a brain - could miss that opportunity! We pictured her having braces in our mind's eye so much and so often, that THAT became "reality" for us, to the point that it encroached on our memory of the scene, and emblazoned itself thereon.
In fact, I think now I'll go with this. After all, the "alternative" (see what I did there?) is that we crossed from a universe in which the director remembered to stick braces on her, into a universe in which he simply forgot, or didn't think of it at all. And if he thought of it one universe, why wouldn't he think of it in all of them?