Recently, I tested some parameters in Web.config to see how a download functionality would work.

maxRequestLength was changed from 20000 to 40000.

maxAllowedContentLength has been added to 4000000000.

I see, now, that on occasional basis, when a download occurs, I have this:

The remote host closed the connection. The error code is 0x800703E3.

at System.Web.Hosting.IIS7WorkerRequest.RaiseCommunicationError(Int32 result, Boolean throwOnDisconnect)
at System.Web.Hosting.IIS7WorkerRequest.ExplicitFlush()
at System.Web.HttpResponse.Flush(Boolean finalFlush, Boolean async)
at System.Web.HttpResponse.End()