Does this look like gmail is cracking down on piracy? Extra funny this is just them sending it to their kindle.
Also, Anna’s Archive linked me to a site for getting around this for Kindle but I forget + bookmarked on my laptop. Will edit this if I find it
What you can probably do is create an encrypted archive and selecting the checkbox that hides filenames. It’s what I usually do in that type of case.
It should prevent gmail from knowing what is in the archive.