The image displays in articles, and thumbnails at all resolutions /except/ the one on the file page. Problem exists with multiple versions of the image, both cropped/rotated, and the source version. Suspect someone needs to look at the log to see why it's breaking, as I can't find any issue with the file.
I went to https://upload.wikimedia.org/wikipedia/commons/thumb/1/1a/George_Childs_Dowlais_Ironworks_1840.jpg/800px-George_Childs_Dowlais_Ironworks_1840.jpg?somerandomstring then went to https://commons.wikimedia.org/wiki/File:George_Childs_Dowlais_Ironworks_1840.jpg?action=purge
That seems to have worked for that size (triggering a regeneration of that thumbnail).
Problem exists with multiple versions of the image
Which other sizes are affected?
Sorry, I did not mean that it affected the other thumbnail sizes, but that when I uploaded other versions of the same file with a slightly different crop that they had the same problem. Every other level of thumbnail, and use in articles, worked for every version, just not the one on the file description page.