Problem with bulk insert of documents - Java SDK 2.5

Hi there.
I am testing Couchbase Java SDK 2.5 and Couchbase Server Community Edition. I’ve tried to bulk insert a lot of document using Observable RxJava but sometimes i got:

com.couchbase.client.core.endpoint.AbstractGenericHandler$KeepAliveResponseAction onError
AVVERTENZA: [/ ][KeyValueEndpoint]: Got error while consuming KeepAliveResponse.
java.util.concurrent.TimeoutException
at rx.internal.operators.OperatorTimeoutBase$TimeoutSubscriber.onTimeout(OperatorTimeoutBase.java:177)
at rx.internal.operators.OperatorTimeout$1$1.call(OperatorTimeout.java:41)
at rx.internal.schedulers.EventLoopsScheduler$EventLoopWorker$2.call(EventLoopsScheduler.java:189)
at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(Unknown Source)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

After this exception the insertion procedure keeps on, with occasional occurrences of the above exception, until the following exception appears and the execution ends :

Exception in thread “main” java.lang.RuntimeException: com.couchbase.client.core.RequestCancelledException: Request cancelled in-flight.
at com.couchbase.java.BulkJsonToCouchbaseDB.lambda$0(BulkJsonToCouchbaseDB.java:163)
at java.util.ArrayList.forEach(Unknown Source)
at com.couchbase.java.BulkJsonToCouchbaseDB.readZippedAndInsertInCouchbase(BulkJsonToCouchbaseDB.java:102)
at com.couchbase.java.BulkJsonToCouchbaseDB.main(BulkJsonToCouchbaseDB.java:75)
Caused by: com.couchbase.client.core.RequestCancelledException: Request cancelled in-flight.
at com.couchbase.client.core.endpoint.AbstractGenericHandler.handleOutstandingOperations(AbstractGenericHandler.java:546)
at com.couchbase.client.core.endpoint.AbstractGenericHandler.handlerRemoved(AbstractGenericHandler.java:527)
at com.couchbase.client.deps.io.netty.channel.DefaultChannelPipeline.callHandlerRemoved0(DefaultChannelPipeline.java:616)
at com.couchbase.client.deps.io.netty.channel.DefaultChannelPipeline.destroyDown(DefaultChannelPipeline.java:868)
at com.couchbase.client.deps.io.netty.channel.DefaultChannelPipeline.destroyUp(DefaultChannelPipeline.java:834)
at com.couchbase.client.deps.io.netty.channel.DefaultChannelPipeline.destroy(DefaultChannelPipeline.java:826)
at com.couchbase.client.deps.io.netty.channel.DefaultChannelPipeline.access$700(DefaultChannelPipeline.java:43)
at com.couchbase.client.deps.io.netty.channel.DefaultChannelPipeline$HeadContext.channelUnregistered(DefaultChannelPipeline.java:1276)
at com.couchbase.client.deps.io.netty.channel.AbstractChannelHandlerContext.invokeChannelUnregistered(AbstractChannelHandlerContext.java:176)
at com.couchbase.client.deps.io.netty.channel.AbstractChannelHandlerContext.invokeChannelUnregistered(AbstractChannelHandlerContext.java:162)
at com.couchbase.client.deps.io.netty.channel.DefaultChannelPipeline.fireChannelUnregistered(DefaultChannelPipeline.java:811)
at com.couchbase.client.deps.io.netty.channel.AbstractChannel$AbstractUnsafe$7.run(AbstractChannel.java:698)
at com.couchbase.client.deps.io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:399)
at com.couchbase.client.deps.io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:443)
at com.couchbase.client.deps.io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:131)
at com.couchbase.client.deps.io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:144)
at java.lang.Thread.run(Unknown Source)

What could be the problem?