As of 7.47.0, by default the Viewer now automatically suspends the render loop when nothing would otherwise visually change frame to frame. This is intended to minimize resource pressure when many Viewers are used on a page, as well as reduce power usage on battery constrained devices (e.g. mobile).
It’s tricky to get the logic correct around this, so if you see any issues where something doesn’t seem to render correctly, but then does render correctly when you do something like move the camera, then it’s a bug and please let us know!
This feature can also be disabled by adding the render-when-idle attribute: Viewer HTML Element Interface | Babylon.js Documentation