Application Manager stops monitoring

Last week Applications Manager stops monitoring of all items. Normally there are this picture what shows "Today's Availability" but last week there were just "There is no data available at this moment.". This was in all kind of monitors. Appmanager didn't inform me anything about it couldn't collect data. It just shows green light. After restart of Application Manager it works now. I didn't find anything odd from logs than this

WARN 23 Jun 11:06 [com.sshtools.j2ssh.transport.HostKeyVerification] [?:?] - Host file is not writeable.
WARN 23 Jun 11:06 [com.sshtools.j2ssh.transport.TransportProtocolInputStream] [?:?] - Socket InputStream is EOF

Before that there are lot of these kind of messages

WARN 23 Jun 10:51 [com.sshtools.j2ssh.transport.HostKeyVerification] [?:?] - Host file is not writeable.
FATAL 23 Jun 10:51 [com.sshtools.j2ssh.transport.TransportProtocolCommon] [?:?] - The Transport Protocol thread failed
java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at java.util.ArrayList.RangeCheck(Unknown Source)
at java.util.ArrayList.remove(Unknown Source)
at com.sshtools.j2ssh.transport.SshMessageStore.nextMessage(Unknown Source)
at com.sshtools.j2ssh.transport.TransportProtocolCommon.processMessages(Unknown Source)
at com.sshtools.j2ssh.transport.TransportProtocolCommon.startBinaryPacketProtocol(Unknown Source)
at com.sshtools.j2ssh.transport.TransportProtocolCommon.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

What is the meaning of this "FATAL" warning and why it makes Applications manager to go nuts? And particularly, why Appmanager didn't inform me that it couldn't collect data anymore?

Thanks.

-Heikki