L Parry

Please note, cured villagers will only have a discount if they have XP when they are infected. If they have no XP when infected, they will not offer a discount when cured. 

I don't know if this is intended behaviour or not but this appears to be the mechanic behind villagers offering discounts when cured after infection.

Just ran into this on 1.19. Even though I have all the items in my inventory it won't allow me to auto craft. However I can make the dispenser by manually crafting it.

To fix this issue, trade with the villager before infecting. If they have experience they will not pop out of boats /minecarts. 

For clarification. I'm playing on Normal in a Realm. In normal there is a 50/50 chance of villagers being infected. Naturally spawned zombie villagers can be cured and they will have discounted trades. Villagers created from a breeder will not have discounted trades when cured. To resolve this, I had to trade with the villager once to give them experience then infect them. After this they had discounts when cured.

Nitwits, when created by a breeder can be infected. When cured they often come back as a normal villager. I traded with one, then luckily it was infected instead of being killed and it had discounted trades. 

The problem seems to be with "clean" villagers. I.e., ones produced from a breeder. 

Edit - I captured a naturally spawned zombie villager and it did not have discounts. This was not present in 1.16 as 3 of my trading villagers are cured zombie villagers that spawned in a zombie village. It appears that the villager must have experience before being cured for discounts to appear. 

I've found a work around for this on realms. Trade with the villager before infecting so they have some experience. After this they will not pop out of the minecart when they finish curing. They will also have their trades discounted.