Splash screens never clear on oculus.
Testing in 4.14 it seems like UOculusFunctionLibrary::HideLoadingSplashScreen() is never called, maybe still the case in newer versions? Was unable to clear a splash screen in 4.15, but didn't debug the code in 4.15
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-41124 in the post.