FVector ActorLocation = GetActorLocation();
UE_LOG(LogTemp, Log, TEXT("Actor location: %f"), ActorLocation);
You can't log an FVector directly. You need to convert it to an FString and then use %s (not %f) and finally operator* for dereferencing.
This should work
UE_LOG(LogTemp, Log, TEXT("Actor location: %s"), *ActorLocation.ToString());