You could try adding branches checking by bool return values from function.
These modules encapsulates method LineTraceSingle( ) that just returns true if hits something.
This could solve problem or at least minimize “undesired” behaviour.
I guess pro way to do this should be create a Blueprint function that breaks HitResult and gets PhisicalMaterial you hit, comparing it to some Material that you should just apply on “walkable” surfaces, if they’re equal returns true to you use on a branch like shown on my suggestion.
I apologize by lack skills to make a Blueprint graph from function you really need. 