No scene preview in Puzzles.

I am still using 4.20, as it is the latest version I paid for. I have been using it with Blender 3.3.6, and it has been fine until just recently, when trying to create new apps, and then load the puzzle preview. Even with a brand new app, nothing changed in the blend file, etc; the preview window shows a transparent background with no objects at all, as if there is no file to show. Not even the default Verge3D cube.

It is strange, because I have other older apps that have puzzles which do load the preview when I open the puzzles editor.

I am using Firefox as my default browser, which has always been the best choice in the past.