Keyframe Issues

So I’m currently doing a sprite keyframe animation, and I’m having this one problem with the keyframes where the arm I’m trying to move kind of moves up in the middle of the motion, I guess is how I could explain it? I’ll provide a few screenshots to hopefully try and convey whats happening.

because it should just be going from the first picture to the last picture, because I set the blue peg to be on the part between the shoulder and the body, but it goes up instead in the middle, and i’m not entirely sure why that is. It’s probably something to do with the keyframe path, but I’m not sure what about the keyframe path is causing it to do that, so if anyone has any input on this please do let me know. Cheers.