Custom routes for custom non content pages break backoffice. When i add custom mvc or http routes to RouteTable - halph of backoffice start using /{myroute}/ for api, so it just produces 404 and simply not working. My code:

 [ComposeBefore(typeof(ServicesComposer))]
    public class UserComposer : IUserComposer
    {
        public void Compose(Composition composition)
        {
            composition.Components().Append<RouteComponent>();
            composition.Components().Append<BundleComponent>();
        }
    }

public class RouteComponent : IComponent
    {
        public void Initialize()
        {
            RouteConfig.Register(RouteTable.Routes);
            //GlobalConfiguration.Configure(WebApiConfig.Register);
        }

        public void Terminate()
        {
            //throw new NotImplementedException();
        }
    }

public static class RouteConfig
    {
        public static void Register(RouteCollection routes)
        {
            //routes.MapControllerAttributeRoutes()

            routes.MapRoute(
              name: "Default",
              url: "mvc/{controller}/{action}/{id}",
              namespaces: new string[] { "XX.xxx.Controllers", "XX.xxx.Hijacking.Controllers" },
              defaults: new
              {
                  Controller = "CustomTour",
                  action = "Index",
                  id = UrlParameter.Optional
              });
        }
    }

I have added custom namespaces for routes, but umbraco just start using my route in backoffice and doesnt work anymore.

any idea why it happens and how to solve? I cant use .MapUmbracoRoute as need custom MVC, not based on real content pages.

Link to issue on Umbraco-CMS github: https://github.com/umbraco/Umbraco-CMS/issues/6045