craftbukkit/nms-patches/net/minecraft/network/protocol/PlayerConnectionUtils.patch

--- a/net/minecraft/network/protocol/PlayerConnectionUtils.java
+++ b/net/minecraft/network/protocol/PlayerConnectionUtils.java
@@ -7,6 +7,11 @@
 import net.minecraft.util.thread.IAsyncTaskHandler;
 import org.slf4j.Logger;
 
+// CraftBukkit start
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.network.PlayerConnection;
+// CraftBukkit end
+
 public class PlayerConnectionUtils {
 
     private static final Logger LOGGER = LogUtils.getLogger();
@@ -20,6 +25,7 @@
     public static <T extends PacketListener> void ensureRunningOnSameThread(Packet<T> packet, T t0, IAsyncTaskHandler<?> iasynctaskhandler) throws CancelledPacketHandleException {
         if (!iasynctaskhandler.isSameThread()) {
             iasynctaskhandler.executeIfPossible(() -> {
+                if (MinecraftServer.getServer().hasStopped() || (t0 instanceof PlayerConnection && ((PlayerConnection) t0).processedDisconnect)) return; // CraftBukkit, MC-142590
                 if (t0.isAcceptingMessages()) {
                     try {
                         packet.handle(t0);
@@ -36,6 +42,10 @@
 
             });
             throw CancelledPacketHandleException.RUNNING_ON_DIFFERENT_THREAD;
+            // CraftBukkit start - SPIGOT-5477, MC-142590
+        } else if (MinecraftServer.getServer().hasStopped() || (t0 instanceof PlayerConnection && ((PlayerConnection) t0).processedDisconnect)) {
+            throw CancelledPacketHandleException.RUNNING_ON_DIFFERENT_THREAD;
+            // CraftBukkit end
         }
     }
 }