The reason is that the 'https://viewer.babylonjs.com/assets/environment/EnvMap_3.0-256.env' is missing.
As seen here - Testing BabylonPress 3D Suite - BabylonPress - only the default template is broken.
It may affect a lot of sites which use <script src="https://cdn.babylonjs.com/viewer/babylon.viewer.js"></script> etc.