Hi,

We have an Umbraco 8.1.5 web site that is occasionally crashing on random pages while trying to render any one of a number of different macros.

The problem occurs in Umbraco.Web/Mvc/ControllerExtensions.RenderViewResultAsString, which contains this loop: -

            foreach (var v in viewResult.ViewEngineCollection)
            {
                v.ReleaseView(controller.ControllerContext, viewResult.View);
            }

For some reason, one of the instances of IViewEngine in this collection is NULL (and we have so far been unable to figure out why); this throws a null object reference exception.

Has anyone seen anything like this before ?