There's a known issue that when the thumbnail server gets overloaded it freezes. Our new hardware will fix this issue.
There's really not much we can do about that. People need to contact their ISP and try to contest the block.I just wanted to point out that some British ISPs block the main image server (I think it's facdn?) on the basis that the site hosts violent or extremist content.
So thumbnails might be visible, but if you view the submission there's just a blank space.