Sync() calls don't make the default AGKSplash.png display. That image is handled by the initialization stuff in AGK.
I can get my own splash in the correct orientation displayed once the app gets past the AppGameKit stuff and starts the app::Loop() method (Tier 2) or the first couple of lines of code (Tier 1).
On Android the app assumes portrait mode. I might look into the core Android files and see if there is a way to force it to landscape at the very start.
On Apple, setting the correct stuff in the Xcode project .plist file will force the app to start in the correct orientation. You can also make it appear to be in landscape by creating the default-portrait.png file originally as landscape and then rotate it one way or the other so that it looks like it is in portrait. I've attached an image (my WIP, which is very close to done) as an example.
And I'm not sure I've made the test of AGKSplash.png 'looking' landscape but being portrait. But I suspect it will be an issue either way.
Apple allows files for all orientations as the default images, so it will always show the correct one on startup (before the AppGameKit app code kicks in).
Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master