In a few projects now (with and without animation), when reuploading a model with additional meshes, sometimes they don’t appear. I haven’t done a deeper analysis on how to reproduce this.
I export fbx from Blender and upload them in a .zip using the website.
If somebody from staff wants to look at it, it’s the model called “Attisholz 210827 - Duplication”.
(Image on the top is in Sketchfab, below is in Blender)