Blender 3.0 Asset Browser Not Rendering Thumbnail 14/15 Items

I’m find that very few assets will render a thumbnail when I press the generate thumbnail button. 1 out of 15 items I tried would render thumbnail. The rest just remain as generic doc icons.

I downloaded a few assets from BlenderKit, arranged them in a new project, saved project as “assets.blend” and then proceed to mark as asset, each model. They appear as shown below with no useful thumbnails. Only a two had thumbnails. I was able to get two more to force render a thumbnail when I selected them and hit the render thumbnail. Bug?