Why does my “Update Spline” component
look different than yours?
On Begin Play calls a function belonging to the spline component. Call the the Custom Event that was created in the graph instead - here, it was (unfortunately!) also named UpdateSpline and this is where the confusion is coming from. My bad. Perhaps rename the custom event to something more meaningful to avoid similar names and call that.
Also, your timeline will not play. When you open it (by double clicking, do ensure that Autoplay and Loop are ticked:
Do tell if you got it to work.