Were you able to solve this problem? I'm encountering it as well and I hit the runtime error whether I register an itemClass or a nib. This is a big problem if I try to implement an NSCollectionView in a framework since AppKit seems to try to load the nib from the app bundle and not the framework bundle, and there's no way to configure it to use the framework bundle. My workaround was to add the nib to the target project instead of defining it in the target framework.

I've noticed this bug as well in my app. During my investigation, I tried creating a test project that simply had two NSTextViews side-by-side and it exhibits the bug. When the test app launches, the first text view has the IP flashing, but if I click on the other text view to start editing there, it disappears. As soon as I start typing, the IP shows up. It's incredibly frustrating as it does make it seem like you're not able to type, but you can. For context, I've created the two NSTextViews programmatically by first calling NSTextView.scrollableTextView() to return an NSScrollView and then casting its documentView as an NSTextView. I don't know when this bug started showing up either. I'm running 13.4.1 (c).

Were you fully able to resolve this? I am seeing the same error when uploading my macOS app to the App Store. I'm using the iOS-style App Group ID and I can certainly resolve the issue by prefixing the App Group with my Team ID. However, this is problematic because users with existing installations of my macOS app will have their data in the Group Container folder that uses the iOS-style App Group ID. I'm using the Xcode managed Profile for the provisioning profile and I've inspected it and it does appear that the com.apple.security.application-groups key with value group.com.XXXX exists in there. I'm not sure what else I'm missing here or if iOS-style App Group IDs just no longer works?