If you don’t know what Fast Sketch Cleanup plugin is, here’s a blog post describing it in detail: https://krita.org/en/posts/2024/fast_sketch_background/. In short, it’s a neural network-based filter similar to Edge Detection or Engrave that is supposed to clean up a sketch and create lines that can be used as a base for a lineart or help with coloring.
The images don’t render for me in this one, either.
I’m pretty sure this is a you problem, so posting it in the comments for every post you notice it in isn’t going to help anything.
Hmm I can’t see the images either, so maybe there is a problem. But is true that one can see the images in the original post too 
@ngraham, I’ve had 5 people agree with me thus far, and it’s solely affected certain posts:
One of them was fixed because it was a code problem in that person’s transferrer:
I’m noting it because if, in the future, some of these are fixed but others aren’t, like before, it demonstrates which are affected by which problem. Considering that you can see these but not I, I doubt that bugs.kde.org/show_bug.cgi?id=496306 applies here either.