HTTP HEAD requests to MVC form rendering may fail with a 404 Not found error and an unhandled exception. The following message can be found in the log reports:
Exception: System.Web.HttpException
Message: A public action method 'Index' was not found on controller 'Sitecore.ExperienceForms.Mvc.Controllers.FormBuilderController'.
Source: System.Web.Mvc
at System.Web.Mvc.Controller.HandleUnknownAction(String actionName)
at System.Web.Mvc.Controller.ExecuteCore()
at System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext)
at Sitecore.Mvc.Controllers.ControllerRunner.ExecuteController(Controller controller)
at Sitecore.Mvc.Controllers.ControllerRunner.Execute(TextWriter writer)
at Sitecore.Mvc.Pipelines.Response.RenderRendering.ExecuteRenderer.Render(Renderer renderer, TextWriter writer, RenderRenderingArgs args)
...