Same here. Trying that, I export from Blender some simple object as GLB or OBJ, but same result. It showed few times, but after that it shows just as box. Got laptop with NVIDIa GTX1650 with 4GB, 32 GB ram.
Trying different settings and purge, but seems just random when it shows or not.
I tested it with powerful enough computer, and had same issue. In my case I used Blender to export obejct, not sure if that's the reason. But it worked caouple time for moment.
Okay, got it working. With my laptop, I need to make laptop's display as main display. When I was using external display as main main display looks like Mercury or something wasn't work right. So exporting from Blender as glb and gltf works so far. 😄
Here's what's happening. When you import a 3D model and add it to a comp, AE submits the 3D model and its transforms/parameters to our 3D engine (Advanced 3D). The engine loads the 3D model asynchronously and, while it's loading, we render a placeholder box in its place. Once the 3D model is finished loading, we re-render the model without the placeholder. Note that some 3D models are very complex (e.g. lots of faces), so loading can take a little while. If you continue to see problems with placeholders, DM me specifics, and I will investigate them. Thanks.