Sometimes on the first launch of the game after install, the launch image will be a cropped portrait drawn in landscape orientation, on the left side of the screen, with the top and bottom getting cropped by the screen borders and the left end of the screen black before switching to landscape.
1) Create a new 3rd Person template project
2) Disable Portrait mode support under iOS Project Settings
3) Launch project on an iOS device
4) Occasionally, launch image will briefly appear in Portrait mode before switching to landscape
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-200300 in the post.