Rigidbody.MovePosition doesn't move reliably?

I posted somet$$anonymous$$ng similar a w$$anonymous$$le back, and the answer I got (w$$anonymous$$ch was to put it in fixedUpdate) helped the problem a lot, but not completely. When I use Rigidbody.MovePosition or Rigidbody.MoveRotation, the object doesn't always move the correct distance. Sometimes it'll move a little farther than it should, or rotate too far around. Does anybody know what may be wrong? Here's my code, thanks for the help!

 if(bIsSpinning == true)
     {
         
         if(spinDirection == "right")
         {
                 rigidbody.MovePosition(rigidbody.position + Vector3(30,0,0) * Time.fixedDeltaTime);
                 rigidbody.MoveRotation(rigidbody.rotation * Quaternion.Euler(Vector3(0,360,0) * Time.fixedDeltaTime));
         }
         else if(spinDirection == "left")
         {
                 rigidbody.MovePosition(rigidbody.position + Vector3(-30,0,0) * Time.deltaTime);
                 rigidbody.MoveRotation(rigidbody.rotation * Quaternion.Euler(Vector3(0,360,0) * Time.fixedDeltaTime));
         }
         if(spinDirection == "up")
         {
                 rigidbody.MovePosition(rigidbody.position + Vector3(0,20,0) * Time.fixedDeltaTime);
 
         }
         else if(spinDirection == "down")
         {
                 rigidbody.MovePosition(rigidbody.position + Vector3(0,-20,0) * Time.fixedDeltaTime * 3);
         }
         else
         {
         }
 }