I tested with macOS 15.1 Beta 4 and can confirm that TestFlight builds are now working as expected (even older ones), including the widgets. Dev builds still have the issues, so still seems like a good idea to migrate the container groups, but at least I should be able to do it transparently to the users. Thanks!

I have an app affected by this in production, using the App Group communicate between the widgets and the app. I've filed feedback FB15161604, but I'll assume that going forward I'll need to bite the bullet and move the App Group. My issue is my users' preferences are trapped in the old App Group. Are there anticipated issues with including both App Groups, but only accessing the old one to retrieve the old preferences? The users will get a permission prompt for the old App Group on the dev and TestFlight builds, but will they also get one on the App Store builds? It affects whether i need to create a migration UI to explain the situation, or can silently do it in background. It would certainly be helpful if the TestFlight releases were consistent with the App Store releases.

I think I found the cause of the problem, on my system anyway... After a bunch of digging around, I found that the case of the folder associated with the XCode group containing my source code didn't match the case on the file system. (ie. the XCode group "Weather" was associated with "/Users/....../Weather" but the folder on the file system was called "/Users/....../weather".) When I used the little folder icon in the inspector to re-associate it with the folder, the case was corrected and whammo all my missing error messages suddenly reappeared. I'm guessing that at sometime along the line of XCode 14 betas, it started caring about case sensitivity, so my project file that used to work fine was now incorrect as far as the linter was concerned. So: Check that the case of the folders associated with your XCode groups match the file system, and use the little folder icon to correct it if they're not. Hope this helps!