SMTP Pool Monitor periodically marks one node down and then back up

I have tried looking at some of the other SMTP Monitor related answers and could not find one specifically related to the issue we are noticing. We have 3 nodes in this pool and the pool is setup with a SMTP monitor with interval of 5 seconds and timeout of 16 seconds. The Local Traffic Log shows the monitor status down and then within a few seconds it shows status up. This occurs throughout the day at different intervals around 5 - 10 minutes. The Exchange Admin does not see any errors or logs on this server. The server appears to be receiving and processing traffic as it should. I ran a tcpdump to capture a failure of the monitor.

 

The capture shows when monitor passes the following: 220 server.domain.com Microsoft ESMTP MAIL Service ready at Wed, 6 Sep 2017 10:54:50 -0400 helo domain.com 250 server.domain.com Hello [172.xx.xx.xxx] quit 221 2.0.0 Service closing transmission channel

 

The capture shows when monitor does not pass the following: 220 server.domain.com Microsoft ESMTP MAIL Service ready at Wed, 6 Sep 2017 10:55:29 -0400

 

It does not get the helo and after 33 seconds is see a few [RST] and then a sequence with a helo.

 

I am trying to determine if this is something related to the monitor on the F5 or on the server side potentially. From what I can tell the tcpdump does not indicate exactly why the helo is not received during those time periods.

 

Thanks in advance.