For me the first thing that comes to mind is Tales from Earthsea. I don’t think it’s excellent or anything and has plenty of problems but people act like it killed their dog. While it has its problems that have been covered extensively, I think it has a beautiful atmosphere and art.
IMO it would have been better received if it wasn’t advertised as an Earthsea adaptation and was just its own thing.
For me, Titan AE was the first Mandela effect. I clearly remember teaser trailers years before its release with a totally different art style. It looked like really good anime. Then once it dropped it was this weird amalgamation of Disney’s Pocahontas and Fox The Simpsons. Still feels like a fever dream.
As I understand it, a couple hundred staff were laid off at the beginning of its final year of production. So a lot of the movie got outsourced instead of made by the people who started the film and did the trailers. Also, more than half the budget was spent before it went into full production. This may partially account for that bizarre discrepancy we had as kids looking at the trailer then seeing the full film.
That’s not the mandala effect of Titan AE. The Mandela effect from that movie is that we all remember that Creed song being in the film but it wasn’t.