I turned a zombie villager into a villager and traded with him for a little. After a few trades, he seemingly stopped giving me discounts randomly, for no reason. It is just one trade (melons) on my farmer which stopped offering a discounted price. Is this a new feature? Or is it something not meant to be? Because this is not the case for any other villager of mine.
When you use one trade offer too much, the villager will punish you and increase the prices. This is intentional and part of the supply and demand system, see MC-146373.