Some of the things that have been pointed out are more of myth than anything.
"Play it again, Sam" - never happened but it is common to hear it. I forget where it originated from but it was some skit done as a parody/tribute to Casablanca which never uttered those words. I think that there's a lot of this "mis-hearing" things that take on a life of their own.
Star Wars', "Luke, I am your father," and "Life was like a box of chocolates," from Forrest Gump may play into this "mishearing" deal. That being said, I saw a video where a guy claimed to have watched Star Wars 500-600 times and only recently had it changed. In my head, if he had it wrong and was that much of a Star War fan then he would have noticed it WAY earlier and he would have been the guy saying, "No.. Everyone thinks it's that way but it's not. It's, "No, I am your father."" That's what you'd think a true fan would do/say. They'd pick up on that little bullshit and correct you.
For Forrest, it can make sense because he's talking about his mom in the past tense and, again, may have been misheard. I'm not saying it was because I, too, have experienced the Mandela effect and it's pretty strange.
Some glaring ones for me:
Chic-fil-a - I remember thinking as a kid that it was an odd spelling but they had great chicken sandwiches and who was I to complain. Now's it's "Chick-fil-a". When I first realized it was "Chick" in the last few years (maybe a decade) instead of "Chic" I thought, "I wonder why they changed their name - stupid marketing people.." I never realized that in the current reality (which, right there, makes me sound crazy) that it had always been, "Chick-fil-a". Let me pose this to you: Wouldn't it be far more likely for me to not remember "chick" as "chic"? It wasn't like "Chick" was a new word or anything and, in context, it makes perfect sense. So, "Chic" would be the outlier. If it were always "Chick", which makes absolute sense, then my mind never would have come up with "Chic".
Star Wars: C3POs leg: It's now silver (well, the lower portion). This is one where, when I first saw it, I thought, "Wow? Why is his leg silver? That isn't the way it's supposed to be.. Stupid Lucas - always fucking with his films!" Apparently, again, in this reality, it has always been sliver. That's a detail I, and my friends, would have definitely picked up on when we were kids. He was always completely gold to us.
The Bible changing is freaky. Never heard the "Wolf and the lamb" even after a few decades of going to church and Sunday school until now. It was always the "Lion and the lamb".
"Mirror, Mirror" vs "Magic Mirror" - this is one which I think is people just saying the wrong thing and enough say the wrong thing to where that's the thing you say. I remember first being corrected on this when Snow White came out on LD in the early 1990s and thinking, "Uh - so that's what she's actually saying..." It also makes more sense to say, "Magic Mirror on the wall," than to say, "Mirror, Mirror on the wall.."
In summary, I actually think something is happening. At the same time, I think people are taking "false memories" of just about anything and attributing them to this.