It appears that, on uploading, WP media library looks for certain spammy-looking filenames, and prevents these files from displaying. Is this a feature? Is it documented anywhere? Can it be disabled? (Googling turns up nothing.)
Explanation. Using a fresh installation of WordPress 4.8.3 on a new domain, I am publishing a book for an author friend. The book contains about a 100 photos taken during his travels. I was happily uploading the images when I noticed that 1 thumbnail was not showing the photo, but a blank, grey square. This was weird, so I tried placing the image in a post, with the same result: the file exists (and it is the same physical file I uploaded, not altered in any way), but the post shows a blank gray area where the image should be.
The file is named - and I hope StackExchange will permit this, now - "chapter_02_img_02_beer_advertisement_1990.jpg". This is indeed what's in the photo: an ad for beer.
So I am thinking maybe an overzealous admin at my host set up some trap, but no - WP does the same exact thing on localhost, using a different theme, and no plugins whatsoever. And sure enough, when I renamed the file to a more innocuous-looking "chapter_02_img_02_ba_1990.jpg" and reuploaded, the problem went away. (But this is a nuisance, now I have to maintain a separate set of files to keep all links healthy.)
Is this a thing in WordPress, or should I be looking elsewhere for the cause?