When using a Line Trace By Channel Blueprint node and setting Trace Complex to True the trace will sometimes not hit anything even though it clearly would have to!
This gif makes it clear, the spline mesh generation goes towards the center of the ball with some randomization in direction. It stop as soon as its generation would penetrate the ball by tracing with Trace Complex:
As you can see it sometimes does not trace anything and then even goes through the whole ball. The ball is the default UE4 sphere.
Here it is working with with trace complex set off:
I also tried this with Capsule Trace By Channel and it had the same bug.