Sending binary messages on the AsyncRemote endpoint throws an error in the log:
21:11:28,747 ERROR [org.xnio.listener] (default I/O-6) XNIO001007: A channel event listener threw an exception: java.lang.IllegalStateException: XNIO000017: Buffer was already freed
at org.xnio.ByteBufferSlicePool$PooledByteBuffer.getResource(ByteBufferSlicePool.java:206)
at org.xnio.ByteBufferSlicePool$PooledByteBuffer.getResource(ByteBufferSlicePool.java:176)
at io.undertow.server.protocol.framed.AbstractFramedChannel.flushSenders(AbstractFramedChannel.java:490)
at io.undertow.server.protocol.framed.AbstractFramedChannel$FrameWriteListener.handleEvent(AbstractFramedChannel.java:793)
at io.undertow.server.protocol.framed.AbstractFramedChannel$FrameWriteListener.handleEvent(AbstractFramedChannel.java:790)
at org.xnio.ChannelListeners.invokeChannelListener(ChannelListeners.java:92)
at org.xnio.conduits.WriteReadyHandler$ChannelListenerHandler.writeReady(WriteReadyHandler.java:65)
at org.xnio.nio.NioSocketConduit.handleReady(NioSocketConduit.java:93)
at org.xnio.nio.WorkerThread.run(WorkerThread.java:539)

This happens after a few minutes and generally the number of errors increase rapidly and we can easily have a 2Go log after a few hours.

Code is:

session.getAsyncRemote.sendBinary(event.asReadOnlyBuffer(), new SendHandler(){
override def onResult(result:SendResult) {
}
})

It worked well with wildly 9.0 alpha 1 but bug appeared with beta 2.

I generally receive a close event on the web socket session after the error logging.