Problem description Since macOS Sequoia, our users have experienced issues with multicast traffic in our macOS app. Regularly, the app starts but cannot receive multicast, or multicast eventually stops mid-execution. The app sometimes asks again for Local Network permission, while it was already allowed so. Several versions of our app on a single machine are sometimes (but not always) shown as different instances in the System Settings > Privacy & Security > Local Network list. And when several instances are shown in that list, disabling one disables all of them, but it does not actually forbids the app from receiving multicast traffic. All of those issues are experienced by an increasing number of users after they update their system from macOS 14 to macOS 15 or 26, and many of them have reported networking issues during production-critical moments. We haven't been able to find the root cause of those issues, so we built a simple test app, called FM Mac App Test, that can reproduce multicast issues
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