CubeTexture from CubeRenderTarget not working in fragment shader

Hi there, I’m trying to use the CubeTexture generated from CubeCamera in a fragment shader with textureCube() function. But I got black screen. When I load a CubeMap with local texture image, the fragment shader works well. The CubeTexture also works great with MeshStandardMaterial. My abstract version of code and issue can be seen here https://codepen.io/Lee-Yuguang/pen/ExOzpdM When it’s working, the object should be blue. Can someone point me the problem in my code please?