On Mobile Previewer and Android, multiple startup movies will play in sequence. However on iOS, only the first movie in the StartupMovies array appears to be playing. It appears that 4.14 brings some changes to DefaultGameMoviePlayer and AppleMovieStreamer, both classes involved in the startup movie sequence.
Thank you for submitting a bug report. I have reproduced the issue and logged it as UE-39585 which you can track on the following link: Unreal Engine Issues. Please be aware that since the issue must be reviewed and prioritized by our development staff, it may be a while before it can be addressed.