Oh no! This is not good. Thank you for letting me know.
The same had happened on my forum. Looking at the post, what I think has happened is that after a few days Discourse has decided that the uploaded poster image and the 3D model are no longer needed so it has deleted them from the server. 
I have ‘fixed’ this temporarily on my site by reuploading the model and the poster but I’m now off to read through the Discourse theme docs to see if I can fix it properly. From the quick scan I did when writing the theme component I saw the docs say that as long as an asset is referenced by a post then it will be kept on the server but obviously the URLs that this component puts in the post are not doing that for some reason. If any other plugin writer can offer advice on this it would be much appreciated… 