I have been using STOMP and sockjs for some time now, but the error below happens at times.

12:57:30.976 [48] [tcp-client-loop-nio-4] INFO  org.springframework.messaging.simp.stomp.StompBrokerRelayMessageHandler - TCP connection failure in session w6s21o5d: failed to forward DISCONNECT session=w6s21o5d
reactor.netty.channel.AbortedException: io.netty.channel.StacklessClosedChannelException
  at reactor.netty.FutureMono$FutureSubscription.wrapError(FutureMono.java:186) ~[reactor-netty-core-1.0.7.jar!/:1.0.7]
  at reactor.netty.FutureMono$FutureSubscription.operationComplete(FutureMono.java:177) [reactor-netty-core-1.0.7.jar!/:1.0.7]
  at io.netty.util.concurrent.DefaultPromise.notifyListener0(DefaultPromise.java:578) [netty-common-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.util.concurrent.DefaultPromise.notifyListenersNow(DefaultPromise.java:552) [netty-common-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.util.concurrent.DefaultPromise.notifyListeners(DefaultPromise.java:491) [netty-common-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.util.concurrent.DefaultPromise.setValue0(DefaultPromise.java:616) [netty-common-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.util.concurrent.DefaultPromise.setFailure0(DefaultPromise.java:609) [netty-common-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.util.concurrent.DefaultPromise.tryFailure(DefaultPromise.java:117) [netty-common-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.channel.AbstractChannel$AbstractUnsafe.safeSetFailure(AbstractChannel.java:1021) [netty-transport-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.channel.AbstractChannel$AbstractUnsafe.write(AbstractChannel.java:882) [netty-transport-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.channel.DefaultChannelPipeline$HeadContext.write(DefaultChannelPipeline.java:1367) [netty-transport-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:717) [netty-transport-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:709) [netty-transport-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:792) [netty-transport-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:702) [netty-transport-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.handler.timeout.IdleStateHandler.write(IdleStateHandler.java:304) [netty-handler-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:717) [netty-transport-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.channel.AbstractChannelHandlerContext.invokeWriteAndFlush(AbstractChannelHandlerContext.java:764) [netty-transport-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.channel.AbstractChannelHandlerContext$WriteTask.run(AbstractChannelHandlerContext.java:1071) [netty-transport-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:164) [netty-common-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472) [netty-common-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:497) [netty-transport-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989) [netty-common-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) [netty-common-4.1.65.Final.jar!/:4.1.65.Final]
  at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) [netty-common-4.1.65.Final.jar!/:4.1.65.Final]
  at java.lang.Thread.run(Thread.java:829) [?:?]
Caused by: io.netty.channel.StacklessClosedChannelException

The disconnection message is send from frontend as shown below before page reload.

    window.addEventListener("beforeunload", function () {
        client.disconnect(function () {
            log("disconnect websocket..");
        });
    });

No logic is written in backend to handle this spring-stomp handles rest of it.

I have gone through resources in STOMP and there is still no explanation on why or exactly on what scenarios this is happening. What could be the possible reasons for this error.