When I put the media into a page or a slider, I see the 300×250 image on the page or slider, even though the thumbnail is just blank white.
In the Media Library, when I click “Edit” on the blank white thumbnail, I see the 300×250 (full size) image.
If I understand correctly, you want me to paste the URL of the thumbnail into a browser, but I’m not sure where to get the address of the thumbnail from.
Thanks,
Kyle