Yeah, there's no cover metadata, and the current workaround of looking for the first image instead will here point to a probably unrelated gif
.
I can *possibly* tweak that to switch that heuristic to use the first *jpg* image instead, but it still might be wrong.
Since it's been a few years since I touched that code, yeah, a link to the file in a PM would help test that theory (it's encrypted, I can't do anything with it except look at the metadata. If you want to be extra-paranoid and/or you're relying on public storage, put it in a passworded archive, and delete it as soon as I confirm I got it).