What is causing the Mandela Effect?

The Mandela effect is a phenomenon where a large group of people shares the same false memories of a given event or thing.

The Effect is named by Nenson Mandela because some people think he died when he was imprisoned in the 90's while he actually died in 2013. I'm one of those who thought he died in the 90's because I can vividly remember learning about it in school as a kid.

Mandella effects that I'm mostly affected by are:
Darth Vader never said "Luke I'm your father" but "No, I am your father"
Forest Gump famous quote: "Life is like a box of chocolates" is now "Life was like a box of chocolates"
Sinbad genie movie from the ’90s doesn't exist but I remember watching it
Queen - We are the champions song doesn't end with : "we are the champions, of the world...." how I remember it but, "we are the champions..............." -> check it out if you don't believe me

There are many more examples of this effect, and depending on where you are from you wil experience more or less of them.

Here is a list of 20 of the most popular Mandela Effects but I suggest you try to find more examples before you answer the question.

My questions for you are:
What is causing the Mandela Effect?
Which one of them are you experiencing?