To reduce file size, I’m usually optimizing models before upload to have tight control over texture and mesh compression parameters. However, it seems that the files cause an ERROR 13 (CONTACT SUPPORT) and don’t properly upload.
To reproduce, compress any model with
gltf-transform etc1s in.glb out.glb and/or
gltf-transform draco out.glb out2.glb and try to upload that.