ServiceActivationException: Request cannot be dispatched because the virtual application is shutting down

Question

We are having a problem with our virtual application shutting down. Site is running ASP.NET 4.5

Exception summary:

System.InvalidOperationException: Request to the service at '~/Services/ServiceExceptionLogger.svc' cannot be dispatched because the virtual application at '/Site' is shutting down.

Stack trace:

System.ServiceModel.ServiceActivationException: Request to the service at 
'~/Services/ServiceExceptionLogger.svc' cannot be dispatched because the virtual application
 at '/Site' is shutting down. ---> System.InvalidOperationException: Request to the service at '~/Services/ServiceExceptionLogger.svc' cannot be dispatched because the virtual 
application at '/Site' is shutting down.
 --- End of inner exception stack trace ---
at System.Runtime.AsyncResult.End[TAsyncResult](IAsyncResult result)
at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.End(IAsyncResult result)
at System.Web.HttpApplication.CallHandlerExecutionStep.OnAsyncHandlerCompletion(IAsyncResult ar)

Or here is another version of it that shows up in the event logs

Stack Trace:

System.ServiceModel.ServiceActivationException: Request to the service at '~/Services/Service.svc' cannot be dispatched because the virtual application at '/Site' is shutting down. ---> System.InvalidOperationException: Request to the service at '~/Services/Service.svc' cannot be dispatched because the virtual application at '/Site' is shutting down.
   --- End of inner exception stack trace ---
   at System.Runtime.AsyncResult.End[TAsyncResult](IAsyncResult result)
   at System.ServiceModel.Activation.HostedHttpRequestAsyncResult.End(IAsyncResult result)
   at System.Web.HttpApplication.CallHandlerExecutionStep.OnAsyncHandlerCompletion(IAsyncResult ar)

Anyone have any ideas or seen this before? Seems to happen quite frequently on one of our environments, like 10+ times a day. On the QA environment its not happening at all. Idle timeout is set to 20minutes on both environments. Reason for 20 minute timeout is to avoid wasted memory

Update 1: Found some supplementary information on logging app pool recycles here https://webmasters.stackexchange.com/questions/17630/which-event-log-file-does-iis-7-app-pool-log-to/17633#17633?newreg=d562bf378cc545b49a7ea8f2a3c1b48d

Update 2: Apparently the app pool is not recycling when the above exception occurs. We are watching the process in task manager and it is not shutting down or reducing the memory when this exception occurs. Also, no log entry occurs (see update 1) when this exception happens

Answer 1

After escalating this to Microsoft support, we think this issue is a bug .NET 4.5.1. It happens most often when running in integrated mode, but also occurs in classic mode, although much less frequently. We haven't been able to pinpoint the actual case or problem but it doesn't seem to be occuring on older .NET runtimes.