I'm not sure if Discourse does something to the images on upload.
What happens in you download the uploaded file and display it in html? I tried and it worked.
I don't see either, but it looks like the page is still loading, but it's been a long time. Inspect says "Could not load the image" on both images.
It did finally load, and I see the jpg, but not the png.
If I try and view the png file directly, Firefox says: The image "http://3dp-site.alexbelinsky.com/thermateur-mobile.png" cannot be displayed because it contains errors.
Could you zip the file and upload here? That way we should get the file as you have it.
Actually, I did manage to download it from your site...