I have reported this before, but It seems just a bit too weird. Raku and I have noticed that we aren't getting any custom enchants when we enchant anymore. When I reported this before, Jordan got Venom 6 pretty quickly when he tested it, but Raku and I have enchanted a good amount of books since then (I myself have enchanted a couple chests worth of them) and still haven't received any custom enchants. About a year ago I used to get a variety of low level CE and some higher / better ones from enchanting way less books from what I have done now. It just doesn't seem like we are extremely unlucky at this point (but we may be still THAT unlucky), as it seems more of like a permissions or 1.13 issue.