I don’t know if it’s gonna help you, but epic had improved a tooltips for “LocomotionAngle” and “LocomotionDirection” in 5.5+
LocomotionAngle now says : The character locomotion angle (in degrees) relative to the specified RotationAxis. This will be used in the following equation for computing the orientation angle: [Orientation = RotationBetween(RootMotionDirection, LocomotionDirection)] In most cases, this is the difference between the Velocity of the Movement Component and the actor rotation (obtained via CalculateDirection)
LocomotionDirection : The character movement direction vector in world space. When set, this vector is used to compute LocomotionAngle automatically. When not set, the LocomotionAngle input should be used instead. In most cases, this vector is the same as the Velocity vector of the Movement Component.