If the stash server does not respond properly the job will hang and never finish. The job will not be possible to abort as well, only a restart of the jenkins server will finish the job.

We got this once against our real bitbucket server, but have reproduced it against a dummy server which accepts the connection but doesn't answer anything on the POST-message.

stack trace at the hanged state:
java.net.SocketInputStream.socketRead0(Native Method)
java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
java.net.SocketInputStream.read(SocketInputStream.java:170)
java.net.SocketInputStream.read(SocketInputStream.java:141)
sun.security.ssl.InputRecord.readFully(InputRecord.java:465)
sun.security.ssl.InputRecord.read(InputRecord.java:503)
sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:973)
sun.security.ssl.SSLSocketImpl.readDataRecord(SSLSocketImpl.java:930)
sun.security.ssl.AppInputStream.read(AppInputStream.java:105)
org.apache.http.impl.io.SessionInputBufferImpl.streamRead(SessionInputBufferImpl.java:139)
org.apache.http.impl.io.SessionInputBufferImpl.fillBuffer(SessionInputBufferImpl.java:155)
org.apache.http.impl.io.SessionInputBufferImpl.readLine(SessionInputBufferImpl.java:284)
org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:140)
org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:57)
org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:261)
org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:165)
org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:167)
org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:272)
org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:124)
org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:271)
org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:184)
org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:88)
org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184)
org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82)
org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:107)
org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:55)
org.jenkinsci.plugins.stashNotifier.StashNotifier.notifyStash(StashNotifier.java:636)
org.jenkinsci.plugins.stashNotifier.StashNotifier.processJenkinsEvent(StashNotifier.java:251)
org.jenkinsci.plugins.stashNotifier.StashNotifier.perform(StashNotifier.java:208)
hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:782)
hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:723)
hudson.model.Build$BuildExecution.post2(Build.java:185)
hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:668)
hudson.model.Run.execute(Run.java:1763)
hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
hudson.model.ResourceController.execute(ResourceController.java:98)
hudson.model.Executor.run(Executor.java:410)