Babylon graphic is no longer being rendered all of a sudden

Bugs
7

I miss in your code where your scene is loaded “scene = createSzene();”

       let engine = new BABYLON.Engine(canvas, true, {
            preserveDrawingBuffer: true,
            stencil: true
        });
        let scene = createScene();

        engine.runRenderLoop(function () {
            if (scene) {
                scene.render();
            }
        });