USDZ models not appearing in Motion

I tried the file you posted (I got the link in the e-mail before it was deleted), and also the old yellow robot.

They both are behaving the same way as in your mac - the image does not show at all in Motion, no matter how it is moved with the controls onscreen or in the Inspector.

I also tried an old free usdz model of the Earth that I had somewhere on my mac, and that is still working correctly - SORT OF. I actually had to move it somewhat to see the whole globe - something that I did not have to do before.

It seems that the "bounding box" for usdz objects may not be computed correctly, resulting in objects being truncated.

I don't think this is a problem with Motion, I think it has to do with the model. I tried the Yellow old robot and it did not render in Motion, as you stated. If you look at the Custom Unit Size parameter, when set to Automatic, the size was massive (couldn't even see the first digit), this means it's being scaled more than 1,000,000 times it's "original" size just to fit in the canvas. When I brought it into one 3D app, the model was 200 mm. Blender could not open it, and I could not see it in Xcode.

FWIW, models from sketchfab often come from an artist working in a software (Maya, Blender, Cinema, etc.) in any of a variety of formats (obj, fbx, glTF, etc.) and sketch fab then runs some process to convert them to USDZ. On top of this, the artist creating the model has to set them up correctly (real world scale, align to ground plane/origin, etc.). I've seen plenty of stuff that is posted on sketchfab that is clearly being made by people with limited 3D workflow knowledge. It can be a great source for content, but it can also be problematic. I've seen objects offset by huge distances from the center, or not real world scale (too big/too small). Additionally, as fantastic as USDZ is, it's still relatively new as a format and if the conversion or writing of a file goes wrong, you are going to need to take it back into a 3D app and fix the problems.

If you really need this item. It might be best to contact the creator. See if they can help you out.

One last thing, this was published 2 years ago, in USDZ development terms, that's actually a lifetime, a lot has advanced. Maybe contacting Sketchfab to let them know the model is problematic as a USDZ?

Yeah, Reality Converter is kind of a must have. I've used it in various ways. It generally works really well with .obj files. For FBX you have to install the appropriate tools, but it can also be a real help. I've had mixed results with gltf files, sometimes you need to use the .glb variant. For those not familiar with Reality Converter, it is a general purpose tool for converting to USDZ, you an also replace textures (note it uses PBR materials which can be a bit different in setup from how many of us learned to texture in the past). I also recommend having Xcode and Reality Composer, as these can be used to open some 3D formats and then convert to USDZ.

But be prepared, as this thread shows, USDZ can be tricky based on a number of factors, so you man not always get the same results between different applications. It's still a format in it's infancy, but seems to be where lots of tools and systems are headed.

Can you post a link to some of these models, so we can try to reproduce the issue?

I have downloaded just a few from sketchfab, some time ago, and those that I tried worked correctly in Motion.

I am away from my mac at the moment but I will try it later today.