I’ve been searching around iTunes Connect and found a mention of an Icon size I hadn’t heard of before. I thought there were only 3: 57 x 57, 114 x 114, and 72 x 72. But the link below mentions 3 more sizes for search results.
Have you included these additional sizes in app submissions?
Here’s a very good summary: Documentation Archive
The uncommon three are for spotlight and settings icons. Most Unity-ade apps won’t have an icon appear in Settings, nor will return spotlight search results. And if your app happens to do either, it’s not a big deal – the larger icon will be scaled down. And if the scaled-down version looks like crap, then you can make a custom version.
512x512
iTunesArtwork
Optional but recommended
File should be in png format, but name it without the .png extension
57x57
Icon.png
App Store and Home screen on iPhone/iPod touch
Required
114x114
Icon@2x.png
Home screen for iPhone 4 and iPod 3rd Gen High Resolution
Optional but recommended
72x72
Icon-72.png
Home screen for iPad compatibility
Optional but recommended
29x29
Icon-Small.png
Spotlight and Settings
Optional but recommended
50x50
Icon-Small-50.png
Spotlight for iPad compatibility
Recommended if you have a Settings bundle, otherwise optional but recommended
58x58
Icon-Small@2x.png
Spotlight and Settings for iPhone 4 High Resolution
Recommended if you have a Settings bundle, otherwise optional but recommended