Going through the logs on one of my v7 sites running on Umbraco Cloud, and I keep seeing this error being logged, with precious little details as to what antecedent is resulting in throwing the error.

There isn't any pattern than I can see in when it happens, or what activity proceeded it.

I have 20-odd other v7 sites running the same code-base on Umbraco-Cloud, and none of them are logging this error, so I'm at a bit of a loss at the moment.

ERROR Umbraco.Core.UmbracoApplicationBase - An unhandled exception occurred
System.InvalidOperationException: The SessionStateTempDataProvider class requires session state to be enabled.
   at System.Web.Mvc.SessionStateTempDataProvider.SaveTempData(ControllerContext controllerContext, IDictionary`2 values)
   at System.Web.Mvc.Controller.PossiblySaveTempData()
   at System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult)
   at System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult)
   at System.Web.Mvc.MvcHandler.<>c.<BeginProcessRequest>b__20_1(IAsyncResult asyncResult, ProcessRequestState innerState)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult)
   at System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult)
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)