I saw a high volume of errors in that Application event log. This error was referring to both autodiscover and '/EWS/Exchange.asmx' and was appearing multiple times per minute.
Event ID: 3There was also this error about OWA.
Source: System.ServiceModel 18.104.22.168
WebHost failed to process a request.
Sender Information: System.ServiceModel.ServiceHostingEnvironment+HostingManager/32001227
Exception: System.ServiceModel.ServiceActivationException: The service '/Autodiscover/autodiscover.xml' cannot be activated due to an exception during compilation. The exception message is: This collection already contains an address with scheme http. There can be at most one address per scheme in this collection.
Parameter name: item. ---> System.ArgumentException: This collection already contains an address with scheme http. There can be at most one address per scheme in this collection.
Event ID: 108The errors in the log began at about 12:15am when someone had done a server reboot. So, something in that reboot triggered the issue. My first thought was updates, but no updates had been applied recently.
Source: MSExchange OWA
Outlook Web App couldn't connect Exchange Web Services due to a configuration error. Response code = "null, webException.Status = SendFailure".
After a bit of research, it turned out to be the bindings for the default web site causing the issue. At some point, someone had added additonal http and https bindings to the default web site. When I removed the additional http and https bindings everything started properly and the errors no longer appeared.
I am guessing that someone added those bindings a long time ago, but they didn't start causing the issue until IIS was restarted as part of the reboot.