Sorry to hear that the image download problem wasn't just me. Glad to hear it was quick to fix, though. And the image referrer fix appears to be actually getting images that weren't being got before, so this could mean that I'm going to come out of this with fewer broken image links than I went into it. So a net positive in the end!
For anyone who may have used FFF to update image-bearing stories in the narrow window of time where this bug was in effect, I recommend the
Quality Check plugin for finding books that might have been damaged by it.
You can set Quality Check's search scope to be the entire library or just selected books.
Under the "Epub structure" menu there is a "Check broken image links" option, it will mark ebooks that have any broken image links in them. If you don't have backups then an "Overwrite always" update may bring back the broken images.