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When a feedback thread is accepted or declined, you shouldn't be able to reply. (https://gyazo.com/207ad52b75fb05fdbb1b9a2a1befafaf) You can lock threads so I think you can do it on the feedback & suggestions part.
Thank you for your suggestion! We are intentionally allowing players to reply to threads that have received decisions. This is to encourage communication and allow players to ask further questions. We want all players to feel heard.