The post you’ve linked to (referring to the problem being ‘wacky local caching’) explains some of it.
For example, that “TRUST ME. That TV? It’s Safe” post - the thumbnail is broke for me on feddit.nl, but it points to a valid image (it expands to a full one, and ‘Open Image in New Tab’ will display the thumbnail version.
If, however, I view the community through Private Browsing (aka Incognito Mode), the thumbnail displays correctly.