I was sure this would have been posted on the forums already, but after searching it really seems like it wasn't. When viewing pixiv #56625335 it says this instead of showing the image:
Only ちょん＊'s My pixiv list can view this.
Send a My pixiv request to join ちょん＊'s My pixiv list.
Is there any way of getting around this? Strangely enough, clicking "My pixiv request" leads to 404 error page.