No thumbnail was displayed for this file after purge few days ago:
This problem does not exist anymore in November 2017 as the file got replaced by a smaller one. For a testcase, use https://test.wikipedia.org/wiki/File:Zionism_9204_Peace_Conference_1920_copy.pdf instead now.
Few days ago I noticed that some thumbnails are missing (most of them were available). After purge all disappeared and attempt to access any of them gives a "maintanance" message. I doubt there is some maintenance action scheduled for this specific file.
I uploaded also a slightly modified version of this file; the same effect.
As noted above, some thumbnails were available on Sep. 7, so the file did render in past.
The file itself can be downloaded (both versions) and renders fine locally.
Any hints what is wrong here?
The file is used in en.wikisource, so all page thumbnail are required.