Custom villagers ask me for less items to trade than they should

I'm having a problem with villager trading. I create a new profession and assign rank-based trades, say 10 apples for 1 emerald. When I enter the game, the villager asks for only one apple for the emerald. Sometimes, he won't even let me trade it if one of the two item slots I'm supposed to give him is empty. I haven't been able to find a solution to this; in case it helps, I'm using a plugin for modding in fabric.