Mandela Effect/Alternative realities
This the belief that the current reality we live in is not the only one happening. Unlike the many worlds theory in theoretical physics, advocates for this idea believe that there are actually signs that show our current reality has been altered or that they have moved from one reality to another without realising. This is sometimes termed the Mandela Effect due to the preposterousness of the belief that Nelson Mandela died at earlier time than he actually did.
Some people attribute this to them living some other kind of other or alternative reality rather than them just having a poor memory. Other common things people point to are the Berenstein Bears books that many people insist were called Berenstain Bears in the other reality, rather than the more rational reason that they're just a bit shit at spelling and remembering things.