Continuous Login Errors on Edge Server from Hub Server

We are running Exchange 2010 with one hub/cas server and 1 edge server and I noticed an odd thing happening in the security event log. Every 30 seconds on the Edge server I will get a login error that originates from the hub server:

Log Name:      Security
Source:        Microsoft-Windows-Security-Auditing
Date:          9/24/2015 2:52:30 PM
Event ID:      4625
Task Category: Logon
Level:         Information
Keywords:      Audit Failure
User:          N/A
Computer:      MailEdge01.example.com
Description:
An account failed to log on.

Subject:
  Security ID:      NULL SID
  Account Name:     -
  Account Domain:       -
  Logon ID:     0x0

Logon Type:         3

Account For Which Logon Failed:
  Security ID:      NULL SID
  Account Name:     
  Account Domain:       

Failure Information:
  Failure Reason:       The NetLogon component is not active.
  Status:           0xc0000192
  Sub Status:       0x80090325

Process Information:
  Caller Process ID:    0x0
  Caller Process Name:  -

Network Information:
  Workstation Name: -
  Source Network Address:   192.168.1.56
  Source Port:      25919

Detailed Authentication Information:
  Logon Process:        Schannel
  Authentication Package:   Microsoft Unified Security Protocol Provider
  Transited Services:   -
  Package Name (NTLM only): -
  Key Length:       0

This event is generated when a logon request fails. It is generated on the computer where access was attempted.

The Subject fields indicate the account on the local system which requested the logon. This is most commonly a service such as the Server service, or a local process such as Winlogon.exe or Services.exe.

The Logon Type field indicates the kind of logon that was requested. The most common types are 2 (interactive) and 3 (network).

The Process Information fields indicate which account and process on the system requested the logon.

The Network Information fields indicate where a remote logon request originated. Workstation name is not always available and may be left blank in some cases.

The authentication information fields provide detailed information about this specific logon request.
  - Transited services indicate which intermediate services have participated in this logon request.
  - Package name indicates which sub-protocol was used among the NTLM protocols.
  - Key length indicates the length of the generated session key. This will be 0 if no session key was requested.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-Security-Auditing" Guid="{54849625-5478-4994-A5BA-3E3B0328C30D}" />
    <EventID>4625</EventID>
    <Version>0</Version>
    <Level>0</Level>
    <Task>12544</Task>
    <Opcode>0</Opcode>
    <Keywords>0x8010000000000000</Keywords>
    <TimeCreated SystemTime="2015-09-24T19:52:30.469590700Z" />
    <EventRecordID>113299</EventRecordID>
    <Correlation />
    <Execution ProcessID="580" ThreadID="816" />
    <Channel>Security</Channel>
    <Computer>MailEdge01.example.com</Computer>
    <Security />
  </System>
  <EventData>
    <Data Name="SubjectUserSid">S-1-0-0</Data>
    <Data Name="SubjectUserName">-</Data>
    <Data Name="SubjectDomainName">-</Data>
    <Data Name="SubjectLogonId">0x0</Data>
    <Data Name="TargetUserSid">S-1-0-0</Data>
    <Data Name="TargetUserName">
    </Data>
    <Data Name="TargetDomainName">
    </Data>
    <Data Name="Status">0xc0000192</Data>
    <Data Name="FailureReason">%%2306</Data>
    <Data Name="SubStatus">0x80090325</Data>
    <Data Name="LogonType">3</Data>
    <Data Name="LogonProcessName">Schannel</Data>
    <Data Name="AuthenticationPackageName">Microsoft Unified Security Protocol Provider</Data>
    <Data Name="WorkstationName">-</Data>
    <Data Name="TransmittedServices">-</Data>
    <Data Name="LmPackageName">-</Data>
    <Data Name="KeyLength">0</Data>
    <Data Name="ProcessId">0x0</Data>
    <Data Name="ProcessName">-</Data>
    <Data Name="IpAddress">192.168.1.56</Data>
    <Data Name="IpPort">25919</Data>
  </EventData>
</Event>

The IP address 192.168.1.56 is the address of our hub/cas server sitting in our main network. The edge server (not a domain join server) sits in our DMZ.

This doesn't appear to be causing any issues and I don't see any messages appearing on either host (other than the security logs). I looked at the firewall and the message seem to coincide with RPC calls on port 50636. I have already tried recreating the certificate for the edge server and the edge subscription.

Is this something that needs fixing or does anyone have any idea why it's happening?