I actually think I have a clue on what's happening. My app is currently only available for iPad, and as soon as I added the iPhone target, the icon started to show up in TestFlight. So maybe that is the issue - there is some type of bug that if the app is only available for iPad, the icon doesn't get processed correctly.
I actually think I have a clue on what's happening. My app is currently only available for iPad, and as soon as I added the iPhone target, the icon started to show up in TestFlight. So maybe that is the issue - there is some type of bug that if the app is only available for iPad, the icon doesn't get processed correctly.