Why does using a ConstructorHelper function cause a crash?

Make sure:

static ConstructorHelpers::FObjectFinder xyz(TEXT("SkeletalMesh'/Game/Dir/abc.abc'"));

is in the constructor, which will resemble something like:

AObjectFinder::AObjectFinder(const class FPostConstructInitializeProperties& PCIP)
	: Super(PCIP)

and be at the top of your cpp (usually)