Bug Game stutters

I don't know why, but in the fps game, when I turn and at the same time I move the character, everything stutters, in the sense that the movement is not so smooth. I also discovered that when the game runs at 30 fps (instead of the standard 60fps) there is no such problem (idk why). this is a problem with my scripts or unity, how do i fix it?

written from a translator (pardon for the mistakes )