No need to register multiple times

proxy/src/main/java/com/velocitypowered/proxy/connection/MinecraftConnection.java

@@ -169,12 +169,16 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
   }
 
   private void installDiscardHandler(ChannelHandlerContext ctx) {
+    if (ctx.pipeline().get("discard") == null) {
       ctx.pipeline().addBefore(MINECRAFT_DECODER, "discard", DiscardHandler.HANDLER);
     }
+  }
 
   private void installDiscardHandler() {
+    if (channel.pipeline().get("discard") == null) {
       channel.pipeline().addBefore(MINECRAFT_DECODER, "discard", DiscardHandler.HANDLER);
     }
+  }
 
   public EventLoop eventLoop() {
     return channel.eventLoop();