6 years on and the silence is still deafening. I notice that NSMatrix is not depreciated as yet, it is only "discouraged in apps that run in macOS 10.8" (https://developer.apple.com/documentation/appkit/nsmatrix)

I experience the same issue. First time I saw this error was when I installed XCode 26.0.1 I suspect this is a bug in Xcode as the error seems to relate to something in different framework.

"Internal inconsistency in menus" errors have appeared upon starting my macOS application. This happened as soon as I upgraded to Tahoe 26.1. My app is not using any custom classes in the menu. This appears to be a bug related to Tahoe.

same for me after upgrading to Tahoe 26.1.