Villagers offering, but not trading enchanted books

Got a librarian villager offering an enchanted book. I click the trade, the emeralds fills in in the trade slot, but no book shows up. If I click the slot the book should've appeared, the villager will shrug (as they do when you talk to a villager without a profession).
I tried trading him paper, to see if it changed anything, but it did not.

I also tried with a second librarian, who offers an enchanted book and a bookshelf. When I click the book deal, the bookshelf deal is placed in the trade slots. Clicking the deal or manually placing the emeralds makes no difference.

I tried 1.14.4 and 1.15-snapshot - with and without optifine/shaders. Restarted Minecraft, and my PC. Travelling to a different dimension, and travelling far away. I've also tried with a full stack of emeralds, to make sure I had enough for the trade.

 

I am aware of MC-149880, but it seems different as none of the enchanted book trades actually gives me a book.

My farmer villagers trades all work fine.