Many years later, but there’s still a related bug to this one even in 4.26.
If you adjust the “Closed Loop” option on the spline component of an actor in the world, then the change will not be visible in the construction script - it will continue to see the old length and the closed loop property in its old state.
However, if you change the option on the blueprint class that the actor is derived from, then that change will be propagated to the world object.
This is probably related to Unreal Engine Issues and Bug Tracker (UE-36728) - though the bug is larger than just that one property not being read.