My game breaks when I load it from another scene (menu scene).

The scene in w$$anonymous$$ch the game is worked fine when I played it on its own, but when I use the "play" button (SceneManager.LoadSceneAsync) it loads the scene and some problems occur. The first problem is: Main camera gets slightly moved (bad). And once I maximize the scene my objects go a lot faster than they should... that renders my game unplayable. So I would really appreciate it if one of you smart fellas knew how to fix t$$anonymous$$s since I wasn't able to find any solutions.