I am new to a lot of things in Unreal, but I suspect maybe the transformations are getting doubled on your character because as I understand it (hopefully this is correct),
When you make an Actor be a Component of another Actor, it is going to move with that master actor unless you specifically design it NOT to. And it won’t alter its own location and rotation values. A component with 0,0,0 location and 0,0,0 rotation will remain at those values no matter what its parent actor is doing, and any changes to those values on the Component are considered relative to the “parent” actor.
So I think that you will get the results you want if you remove the SetActorLocation function call altogether, because then it’s adding transformations relative to the component’s already-moving-with-the-vehicle stuff.
Alternately, you could NOT make the character a component of the vehicle, and just use SetActorLocation to keep him matched to the vehicle’s position.
So I’m not totally sure on this, but I made a test project where the player controls a turret mounted on a spaceship that’s doing barrel rolls and loop-the-loops, and the rotation values on the player controlled component seemed to only be aware of their orientation in relation to the spaceship, unless I specifically told them to base it on world rotation. How truly this applies to your situation will of course depend on how I set the Blueprints up for that project.