Basically, the issue is described in the title.
While surfing through the website via shima.donmai.us and kagamihara.donmai.us, the full images are still pulled from danbooru.donmai.us
For example, that's what happens at https://shima.donmai.us/posts/4572463: https://imgur.com/0tdN4za
That's rather inconvenient for me because danbooru.donmai.us is blocked in my country. Also, this problem seems to be new, because yesterday it was working fine, IIRC.