Fun thing I read a long time ago: when Ubisoft made their version of Tetris. It had stuttering and frame rate issues. Yes. Tetris had performance issues. 😆
I read it was because the game would check your friends list in the background for things, but QA play tested on simple accounts that didn’t have a crapton of friends on them. They didn’t realize what would happen when the game freezes while checking every single friend all the time.
And what was worse it was supposedly in a more main method making it too difficult to patch.