I’m not sure how your using the timeline, in that case it could be due to the interpolation type between beginning and end of a frame.
Otherwise, mite mention these people also missed an important well known step, where you multiply the intended change in value/speed, etc. by the elapsed time since the last frame update(delta time), since the amount of time in between each frame/tick changes with every running tick.
FYI was facing similar problem by coincidence, and so in this example I used a right vector instead of forward vector, which is similar concept but 90° to the right of the forward(front) facing direction.
I did this to correct the import orientation of my skeletal mesh, which faces the Y axis as its intentional front direction.
It would seem skeletal meshes are controlled by their bones and cannot be rotated on their own, unless they are not a root component and can instead follow a parent’s rotation.