Unexplainable WebSocket error

The server works perfectly fine, until at a random moment, it starts throwing hundreds of these per second:

> Aug 09, 2016 10:54:08 AM org.glassfish.tyrus.container.grizzly.client.GrizzlyWriter$WriterCondition$1 onError
> WARNING: Connection closed
> java.io.IOException: Connection closed
> at org.glassfish.grizzly.asyncqueue.TaskQueue.onClose(TaskQueue.java:331)
> at org.glassfish.grizzly.nio.AbstractNIOAsyncQueueWriter.onClose(AbstractNIOAsyncQueueWriter.java:501)
> at org.glassfish.grizzly.nio.transport.TCPNIOTransport.closeConnection(TCPNIOTransport.java:402)
> at org.glassfish.grizzly.nio.NIOConnection.doClose(NIOConnection.java:647)
> at org.glassfish.grizzly.nio.NIOConnection$6.run(NIOConnection.java:613)
> at org.glassfish.grizzly.nio.DefaultSelectorHandler$RunnableTask.run(DefaultSelectorHandler.java:495)
> at org.glassfish.grizzly.nio.DefaultSelectorHandler.processPendingTaskQueue(DefaultSelectorHandler.java:301)
> at org.glassfish.grizzly.nio.DefaultSelectorHandler.processPendingTasks(DefaultSelectorHandler.java:290)
> at org.glassfish.grizzly.nio.DefaultSelectorHandler.preSelect(DefaultSelectorHandler.java:101)
> at org.glassfish.grizzly.nio.SelectorRunner.doSelect(SelectorRunner.java:335)
> at org.glassfish.grizzly.nio.SelectorRunner.run(SelectorRunner.java:279)
> at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:591)
> at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571)
> at java.lang.Thread.run(Thread.java:745)
> Caused by: java.io.EOFException
> at org.glassfish.grizzly.nio.transport.TCPNIOTransport.read(TCPNIOTransport.java:597)
> at org.glassfish.grizzly.nio.transport.TCPNIOTransportFilter.handleRead(TCPNIOTransportFilter.java:75)
> at org.glassfish.grizzly.filterchain.TransportFilter.handleRead(TransportFilter.java:173)
> at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
> at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:284)
> at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:201)
> at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:133)
> at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:112)
> at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
> at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:526)
> at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
> at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
> at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
> at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
> ... 3 more

The seconds previous were just normal:
#### Environment
RAM 8GB
Debian 7.5
#### Affected Versions
[1.12, 1.13]