Random on and off AD clients lose connectivity to the Exchange Server at random times

As of probably a few months ago, I am getting random clients randomly disconnected from my Exchange 2013.  Outlook 2010 will state that it is Trying To Connect and sits there, sometimes for a few moments, and other times for an hour or longer.  This affects AD connected computers and users directly on the network as well as non-AD computers and users off the network.
The certificate is correct.  When the client loses connectivity, if I remote into their machine, they can successfully ping the exchange server with no issues.  Holding down CTRL and right clicking the Outlook icon on the sys tray, I am able to test the AutoDiscover and config successfully.  The connection information, though, states that it is trying to connect.  
I have removed profiles and recreated them.  However in some instances, this does not work and the client does not successfully log onto the Exchange server, i.e. in the auto setup, it has a check for boxes 1 and 2, and then tosses an error that the exchange server is unavailable.  

The local network is pretty flat.  I am on the same switch as the servers.  I have had this happen to me as well.  The network itself goes from a Cisco router to a Fortigate firewall/switch, from there it goes to the server switch and the switches on the individual floors.  
The Exchange  Server is Exchange 2013, running on a Hyper-V Windows Server 2012 R2 Standard.  This Hyper-V machine is hosted on a HP Proliant server, 64Gb of RAM, 3TB of storage, and it is only running that one Hyper-V machine.  The Hyper-V setup itself has plenty of processors and 3/4 of the total RAM assigned to it, but it never really uses that much at all.  

I have tried removing the fortigate as that is the new piece of hardware, just to make sure it wasnt that being goofy, and the problem continues, and yes even with that removed, I was able to ping the server, the autodiscover test completed perfectly, but the user still could not connect.  Recreating the profile eventually fixed it, to only have it show up again the next day.
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taphopeAsked:
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Simon Butler (Sembee)ConsultantCommented:
These are usually network issues. Start with the server, check to see if there any errors there. If the switch is managed, check for errors there as well.
If you get a user who has the problem, plug them in to a different network port. Does the problem follow?

Simon.
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taphopeAuthor Commented:
Well for instance, I am on the same switch as the servers, there are no errors that I see, it just disconnects.  Mine just now disconnected, and is stating that its trying to connect, but I can test autoconfig and it works fine, the connection status shows the mailboxes as not connected.  
Email on smartphones though, never goes down and they access the server via the same network.
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taphopeAuthor Commented:
I should also add that this has been going on for a couple of months now.  The only change network wise was the addition of a Fortigate 100D setup as a switch between the Cisco and the server switch.  I put back the original configuration which was a Cisco to a Netgear GS724TS switch distributing to another GS724TS for the servers and my office.  
Even set back to this original config, the issue still happens. What sucks is that its so random there really is no patter to it.
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Simon Butler (Sembee)ConsultantCommented:
Smart phones connect to the server in a different way. They don't actually stay connected in the same way as Outlook, they retain an underlying connection, but the actual link is completely different.

Does the server have the latest drivers for its network card? Nothing logged on the server or the workstation at the time of the traffic drop at all?

Simon.
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taphopeAuthor Commented:
Not that I am seeing.  The drivers and Windows Updates are good.  Just so I know I am looking at the right spot, where should I check on the Exchange Server as far as event viewer?  On the client, when it drops the Connection Status says disconnected for the mailboxes on Outlook.   During this time, though, the server is pingable, and OWA, ECP, and AutoDiscovery work fine.
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Simon Butler (Sembee)ConsultantCommented:
This is one of those problems that I cannot really tell you what to look for. You just need to look in the Application and System log around the time of the connection drop for anything odd. It is one of those things that when you see it, it will look odd.

Simon.
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taphopeAuthor Commented:
Ok cool.  Ill look again to make sure I didnt overlook anything and let you know.
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taphopeAuthor Commented:
Ok on the client, I am seeing Event 26, Source Outlook, and that the connection to Microsoft Exchange has been lost.  Outlook will restore the connection when possible.  

I do not see the same type of log on the Exchange Server.  
The only real error that I see is a replication error in that it is unable to mount a recovered database (which that one was done on the 2010 server and removed before migration over to the 2013).  
However the timestamp for that event does not match up with the timestamp of the actual connection loss.  
This also happens randomly and by the time I can get to the computer it restores connectivity.
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Simon Butler (Sembee)ConsultantCommented:
Not really sure what else I can suggest. The most common causes of these types of errors are network related, particularly with the random nature of it.
It could be traffic throttling of some description for example, or something interfering with the sessions, but that would all be logged on the Exchange server. The fact that you aren't seeing anything logged pretty much rules out Exchange itself as the cause of the problem - Exchange is very good at logging errors (Even if the errors can be cryptic, you usually get something).

Simon.
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taphopeAuthor Commented:
We ended up having to do a reinstall anyways.  Someone tried the CU5 update and it borked halfway through crashing the entire Exchange install and making it not able to finish the update, thus killing all mail.  
I will look for more issues with this new install.
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