Awesome, that was it. Thanks lucoiso!
For anyone, this is my exact change:
// Changed from:
UAbilitySystemComponent* AbilitySystemComponent;
// Changed to:
UPROPERTY(
VisibleAnywhere,
BlueprintReadOnly,
Category = Abilities,
meta = (AllowPrivateAccess = "true"))
UAbilitySystemComponent* AbilitySystemComponent;