Do You Believe the Reincarnation Story

[Infinite]

Also consider it is quite possible that a lot of us will NEVER make it back to the source. So how does it make sense to create a game that may never ends.

The path of the one is inevitable. It doesn't matter how long it takes. After all, time is an illusion.

And those aspects of the creator that do make it back will be very different than what they were when the left the creator -- due to a trillion years of experience.
Won't this change the essence of the creator?

Evolution is in what is learned through the collection of experiences. It is not a specific identity, but a core of consciousness that feeds on the catalyst. Also remember that there are requirements for harvests at different densities. Thus, those who evolve follow a pattern predetermined by intelligent infinity and Logoi.

Also, the karma doesn't make sense. Do we need to experience an atrocity in order to learn it's a bad thing?
Especially if we forget what happens in past lives.

Whoever forgets is the third density ego, the spirit does not forget. These patterns are recorded.

I am just suspicious if we are told this reincarnation story as a cover story for whatever the truth may be??

Well, many have alternative theories. But I never saw anything that made sense.