So are you spawning these runners at runtime? What you can do is when the runner is spawned, you can give it the info for the spline it’s on BEFORE runtime. Then when the runner is spawned, you can tell it to grab the spline it’s on (because it’s already been set as a variable before game start) and tell that variable (the spline) to get its open variable for “Runner” and set it.
Does that make any sense?
It’s going to be something along those lines. However, without knowing how you’re spawning the Runner instances I don’t know how to point you in the exact direction you need 