There’s no big surprise here. The launch screen is shown at launch time – actually, before launch time – so the font probably hasn’t yet loaded.
You could file a bug if you think you have a compelling use case. But I don’t really think you do. Why are you showing any text in your launch image? It should be much more bare-bones than that – just enough to give the structure of the opening interface, which will be filled in when the opening interface actually appears. A “blank” screen with the same background color as the initial view controller’s background color would be sufficient. You goal is just to provide an alternative to blackness.