The file names people have talked about here are different to the names shown in other places. I submitted an app this morning and just included both naming schemes. I added these new sizes:
Default-414w-736h-landscape@3x.png
Default-Landscape-736h@3x.png
Default-375w-667h@2x.png
Default-667h@2x.png
Hopefully one or the other will work! Won't know for a few days.
