TL;DR: Instead of adding an official iPad icon, I deleted all my icons and added a universal version (1024x1024) which resolved my issue.

Background: I was getting this error because I first made my app forever ago when you had to provide a ton of different icon sizes. At some point, Apple moved to allowing you to provide just one image and they'll resize it appropriately. When I first built my app, I didn't include an iPad version, so I didn't include an iPad icon. On my rebuild, I added iPad support, but not an iPad icon. Either adding an iPad icon or removing all icons and adding a universal icon will solve this issue.