I had to make the following changes to 4.17 to make this work:
Modify IOSToolChain.cs, Line 936
Arguments += Path.GetDirectoryName(DestFile.AbsolutePath.Replace("-IOS-Shipping", "")).Replace("\\", "/") + "\" \"" + \InputFile.AbsolutePath + "\"";
Add IOSTargetSettingsCustomization.cpp, Line 81
new (IconNames)FPlatformIconInfo(TEXT("Icon1024.png"), LOCTEXT("AppIcon_IOS_Marketing", "IOS Marketing Image"), FText::GetEmpty(), 1024, 1024, FPlatformIconInfo::Required);
Assets.car is generated but without the first change above it doesn’t end up in the ipa. The second change enables the user to supply the required marketing image in the project settings.