Paper/nms-patches/PlayerConnectionUtils.patch

--- a/net/minecraft/server/PlayerConnectionUtils.java
+++ b/net/minecraft/server/PlayerConnectionUtils.java
@@ -9,6 +9,7 @@
     public static <T extends PacketListener> void ensureMainThread(Packet<T> packet, T t0, IAsyncTaskHandler<?> iasynctaskhandler) throws CancelledPacketHandleException {
         if (!iasynctaskhandler.isMainThread()) {
             iasynctaskhandler.execute(() -> {
+                if (t0 instanceof PlayerConnection && ((PlayerConnection) t0).processedDisconnect) return; // CraftBukkit
                 packet.a(t0);
             });
             throw CancelledPacketHandleException.INSTANCE;