I’m having a similar problem…I’m using CMake and the standalone icon is there and shows in the iPad’s Finder, but the AUv3 doesn’t show in GarageBand and AUM. I can see it in the Xcode project, in Images.xcassets/AppIcon.
I wonder if some kind of cacheing is going on here, but I’ve deleted the app, rebooted the iPad and rebuilt the app, still, nothing. Any ideas?